Extreme heat and heavy rain in Myanmar could cause disease outbreaks among earthquake survivors camping in the open, global aid bodies warned on Thursday, complicating rescue efforts made difficult by a civil war, as the death toll surpassed 3,000.

Last Friday's 7.7-magnitude quake, one of Myanmar's strongest in a century, jolted a region home to 28 million, toppling buildings such as hospitals, flattening communities and leaving many without food, water and shelter.

Deaths rose to 3,085 on Thursday, with 4,715 injured and 341 missing, the ruling junta said.

The World Health Organization flagged a rising risk of cholera and other diseases in the worst-affected areas, such as Mandalay, Sagaing and the capital of Naypyitaw, while it prepared $1 million of relief supplies, including body bags.

"Cholera remains a particular concern for all of us," said Elena Vuolo, the deputy head of its Myanmar office, pointing to an outbreak last year in Mandalay.

The risk was worsened by damage to about half of healthcare facilities in the quake-hit areas, including hospitals destroyed by the quake in Mandalay and Naypyitaw, she added.

People were camping outdoors in temperatures of 38°C (100°F) because they were too scared to go home, and many hospitals were also setting up temporary facilities there, Vuolo told Reuters from Naypyitaw.

Skin disease, malaria and dengue were among the diseases that could result from prolonged crises, such as in Myanmar, she said.

But conditions could get even tougher for the huge relief effort, after weather officials warned that unseasonal rain from Sunday to April 11 could threaten the areas hardest-hit by the quake.

"I've heard that in the next day or two there are rains (expected)," Titon Mitra, the Myanmar representative of the United Nations Development Programme told Reuters by telephone, during a visit to Sagaing.

"If that hits, we've got people, lots of people now, in temporary shelters, makeshift camps out on the streets, and that's going to be a real problem," he said, also flagging the UN's concerns about an outbreak of waterborne disease.

Despite the devastation, junta chief Min Aung Hlaing will leave his disaster-stricken country on Thursday for a rare trip to a regional summit in Bangkok, state television said.

It is an uncommon foreign visit for a general regarded as a pariah by many countries and the subject of Western sanctions and an International Criminal Court investigation.

Ceasefire

The weather extremes will add to the challenges faced by aid and rescue groups, which have called for access to all affected areas despite the strife of civil war.

The military has struggled to run Myanmar since its return to power in a 2021 coup that unseated the elected civilian government of Nobel laureate Aung San Suu Kyi.

The generals have been internationally isolated since the takeover and Myanmar's economy and basic services, including healthcare, have been reduced to tatters amid the strife.

On Wednesday, state-run MRTV said a unilateral government ceasefire would take immediate effect for 20 days, to support relief efforts after the quake, but warned authorities would "respond accordingly" if rebels launched attacks.

The move came after a major rebel alliance declared a ceasefire on Tuesday to assist the humanitarian effort.

Nearly a week after the quake, searchers in neighbouring Thailand hunting for survivors combed a mountain of debris left after a skyscraper in the capital, Bangkok, collapsed while under construction.

Rescuers are using mechanical diggers and bulldozers to break up 100 tons of concrete to locate any still alive after the disaster that killed 15 people, with 72 still missing.

Thailand's nationwide toll stands at 22.