Bangkok: The United Nations says human traffickers and boat crews routinely kill Rohingya and Bangladesh refugees crossing the Bay of Bengal in a surge of human smuggling and trafficking across South-East Asia.

The UN says as many as 920 people fleeing Myanmar died while crossing the Bay of Bengal in the six months to March from starvation, dehydration and beatings by boat crews amid a surge of human trafficking across South-East Asia.

Refugees have also told the UN that entire boats have sunk but there was no way to verify the reports or how many people were lost.

The UN says that 25,000 people have fled Myanmar and Bangladesh in the first three months of this year alone, in what officials now describe as the largest movement of refugees across the region since the Vietnam War.

In the just-released report the United Nations High Commissioner for Refugees (UNHCR) says hundreds of refugees are alleged to have died in smuggling camps in Thailand in an escalating crisis that has prompted talks among regional governments and a crackdown on traffickers in Thailand, where powerful politicians and local officials have been arrested and 50 police are under investigation.

Thailand's police chief Somyot Pumpunmuang has proposed setting up official camps to shelter Rohingya refugees where they could receive help from international agencies like the UNHCR.

Similar camps were established for Vietnamese boat people in Malaysia and Indonesia following the fall of South Vietnam 40 years ago.

Thailand has also called for a summit of regional nations to discuss the crisis.

The UN report follows the discovery of mass graves in smugglers' camps in Thailand and the arrival in Indonesia and Malaysia of more than 2000 refugees on Sunday and Monday, apparently after traffickers had abandoned them on virtual floating prisons to fend for themselves.

Indonesia's navy on Tuesday towed a boat carrying 400 refugees out of Indonesian waters. The boat had washed ashore early on Monday in the Indonesian province of Aceh.

"We gave them fuel and asked them to proceed. We are not forcing them to go to Malaysia or Australia," navy spokesman Manahan Simorangkir said. "That is not our business. Our business is they don't enter Indonesia because Indonesia is not the destination."

Officials and refugee activists fear that Thailand's crackdown is forcing traffickers to keep thousands of refugees at sea or to drive them deeper into jungle hideouts to avoid detection.

The International Organisation for Migration, a multi-government organisation which supports refugees, says it is extremely concerned for those still on boats who require urgent vaccinations for diseases such as beriberi.

"Search and rescue will be problematic but it must be done – there are up to 100,000 fishing boats in these waters. That's a lot of needles in a very big haystack," an IOM spokesman said.

The UN report says survivors are increasingly lured into life-threatening compromises by smugglers, including false promises of work or claims of initially free passage on the condition that they repay the debt when they find work.

But the report says the refugees then become captives of the traffickers who hold them for ransom at sea.

"The UN agency has noted cases of children being abducted off the streets or while fishing and forced onto boats while, for the most part, people remain unaware that money will be extorted from them later in the journey," it says.

According to the report, one survivor compared his 62 days at sea to a graveyard and said he lost hope of reaching shore alive.

The report says that in 2014, 53,000 people departed from Bangladesh and Myanmar bound for Thailand and Malaysia.

More than a million Rohingya Muslims live in western Myanmar, where they have faced state-sponsored persecution and attacks by Buddhist mobs over the past three years.

The exodus from Myanmar has included woman and children who are initially asked to pay between $US50 and $US300 for passage on a fishing boat, many of which come from Thai ports.

"Some individuals were reportedly forced onto boats in Bangladesh and Myanmar against their will, including unaccompanied children who said they had been abducted by smugglers and marched onto boats at gunpoint," the report said.

The report quotes refugees as telling UN officials that when they were brought to camps in Thailand smugglers demanded up to $US2400 per person to be taken to Malaysia, where many of them have relatives.

The report estimated the smuggling trade across the Bay of Bengal to Malaysia has generated revenue of  $US250 million since 2012.