PORT-AU-PRINCE, Aug 15 (Reuters) - Haiti's hospitals were swamped on Sunday by thousands of injured residents after a devastating earthquake the day before killed at least 1,297 people as authorities raced to bring doctors to the worst-hit areas before a major storm hits.

The 7.2 magnitude quake on Saturday destroyed thousands of homes and buildings in a Caribbean nation which is still clawing its way back from another major temblor 11 years ago and is reeling from the assassination of its president last month.

Southwestern Haiti bore the brunt of the blow, especially in the region in and around the town of Les Cayes. Haiti's Civil Protection Agency said the toll from the disaster had climbed to 1,297 and the hospitals that were still functioning were struggling to cope as some 5,700 people were injured.

In the northwestern city of Jeremie, another badly hit area, doctors treated injured patients on hospital stretchers underneath trees and on mattresses by the side of the road, as healthcare centers have run out of space.

"We do have a serious issue," Jerry Chandler, the head of Haiti's Civil Protection Agency, told Reuters.

"There are very important facilities that are dysfunctional as we speak and those that are functional are receiving an overflow of patients," he said.

The challenge facing Haiti has been exacerbated by the coronavirus pandemic, a severe economic downturn aggravated by fierce gang violence, and a political crisis that has engulfed the troubled nation after the assassination of President Jovenel Moise on July 7.

Churches, hotels, hospitals and schools were badly damaged or destroyed, while the walls of a prison were rent open by the violent shudders that convulsed Haiti. Some 13,694 houses were destroyed, the civil protection agency said, suggesting the toll could rise further.

In Les Cayes, a seafront town of some 90,000 people, rescuers in red hard hats and blue overalls pulled bodies from the tangled wreckage of one building, as a yellow mechanical excavator nearby helped to shift the rubble.

Haiti's Prime Minister Ariel Henry, who flew to visit Les Cayes, praised the dignity shown by people there even in the midst of their suffering.

"They are affected but resilient. They fight to survive," he said, thanking international agencies and foreign governments for their support.

Nearby countries, including the Dominican Republic and Mexico, rushed to send desperately needed food and medicines by air and across Haiti's land border. Colombia sent search and rescue personnel.

The United States dispatched vital supplies and deployed a 65-person urban search-and-rescue team with specialized equipment, said Samantha Power, the administrator of the United States Agency for International Development (USAID).

From the Vatican, Pope Francis urged the international community to show support swiftly. "May solidarity from everyone lighten the consequences of the tragedy," he told pilgrims and tourists at his Sunday blessing in St. Peter's Square.

However, Haiti's government appealed to aid organizations against setting up makeshift camps and urged them to work through the planning ministry, an apparent attempt to avoid the mistakes made following the devastating 2010 earthquake that killed tens of thousands of people.

Many Haitians prepared on Sunday to spend a second night sleeping in the open, traumatized by memories of that magnitude 7 quake 11 years ago that struck far closer to the sprawling capital, Port-au-Prince.

At Port-au-Prince airport, international aid workers, doctors and rescue workers boarded flights to Les Cayes. A U.S. Coast Guard helicopter ferried the wounded.

The rescue and aid efforts will be complicated by Tropical Depression Grace, which is expected to lash Haiti with heavy rainfall on Monday. Some 75 to 100 milliliters of rainfall was expected, which may trigger landslides and cause some rivers to flood, Haiti's Civil Protection Agency said.

"We ask the population to remain vigilant," the agency added.

Thousands of people sleeping in the streets would be exposed to the torrential rains amid a rising risk of water-borne diseases, said Chandler, the head of the agency.

The death toll is expected to rise as telephone network has been down in more remote areas. In difficult-to-reach villages many houses were fragile and built on slopes vulnerable to landslides, said Alix Percinthe, from the Action Aid charity.

He said one local leader had informed him there were 47 deaths in his area not yet reported to regional authorities.

Humanitarian corridor

Footage of Saturday's aftermath posted on social media showed residents reaching into narrow openings in piles of fallen masonry to pull shocked and distraught people from the debris of walls and roofs that had crumbled around them.

Access to the worst-hit areas was complicated by a deterioration in law and order that has left key access roads in parts of Haiti in the hands of gangs. In a video posted on social media, one gang leader said the armed groups had declared a truce along the route to Les Cayes.

Chandler said boats and helicopters were being used to bring in aid but the government was working to establish safe access by road. A first convoy of aid had made it through by land to the region of Les Cayes.

The United Nations called for a "humanitarian corridor" to be established so that aid can pass through gang-held territories.

Following Moise's assassination, which authorities have alleged was carried out by a group of largely Colombian mercenaries and Haitian accomplices, Prime Minister Henry said officials would aim to hold elections for a new president as soon as possible.

However, reports this week suggested that the vote initially earmarked for September would not take place until November. The chaos unleashed by Saturday's disaster is likely to make the task of holding prompt elections harder still.

Haiti has long been politically unstable and Haitians have also suffered from problems stemming from international aid efforts and peace-keeping deployments during the past decade.

A sexual misconduct scandal centering on Oxfam International blighted the record of charity workers in Haiti, while a cholera outbreak linked to U.N. peacekeepers led to thousands of deaths.

The death toll from last week’s 7.2 magnitude earthquake in Haiti has climbed to 2,207, with 344 people missing, according to the country’s civil defence agency.

The death toll increases at a time when relief operations are expanding, and authorities are struggling with security at distribution points. Gangs have hijacked aid trucks and even ambulances, forcing relief workers to transport supplies by helicopter.

Recovery efforts have also been impeded by flooding and damage to access roads, feeding tensions in some of the hardest-hit areas. In places, desperate crowds have scuffled over bags of food.

On Sunday, one of the capital’s most notorious gangsters announced in a social media video that his allied gangs had reached a truce and would assist in relief efforts. If that proves to be true, it might allow an acceleration of relief efforts.

Jimmy Cherizier, alias “Barbecue”, leader of G9 Revolutionary Forces, addressed a Facebook video to the hardest-hit parts of Haiti’s southwestern peninsula.

“We want to tell them that the G9 Revolutionary Forces and allies, all for one and one for all, sympathise with their pain and sorrows,” Cherizier said. “The Revolutionary Forces G9 and allies … will participate in the relief by bringing them help. We invite all compatriots to show solidarity with the victims by trying to share what little there is with them.”

The increase in the death toll was the first since late Wednesday when the government put it at 2,189. The government said on Sunday that 344 people were still missing, 12,268 people were injured and nearly 53,000 houses were destroyed by the earthquake.

The collapse of churches in some of the worst-affected towns and villages of the impoverished Caribbean nation left residents to grieve in open fields.

In the hard-hit city of Les Cayes, meanwhile, some attended outdoor church services on Sunday because sanctuaries had been badly damaged by the earthquake, which was centred on the impoverished nation’s southwestern peninsula.

About 200 worshippers gathered early at the Paroisse Saint-Joseph De Simon Roman Catholic Church on the outskirts of the city for the first Sunday mass since the disaster.

“Everyone was crying today for what they had lost,” said the priest, Marc Orel Sael. “And everyone is stressed because the earth is still shaking,” he added, referring to near-daily aftershocks that have rattled nerves all week.

Aid delivery and rescue teams have been pouring into the country. The USS Arlington arrived from the United States on the weekend, with doctors, nurses, medical devices, two helicopters and 200 Marines.

Additionally, US aid organisation Samaritan’s Purse opened a field hospital in Les Cayes, one of the big cities in the worst-hit area, and took in its first patients.

German aid organisation ISAR Germany has also sent a team of 33 doctors, nurses and orderlies, along with 11 tonnes of material.

The disaster followed a devastating earthquake in 2010 that killed tens of thousands of people.