Nearly 800 "boat people" were brought ashore in Indonesia, but other vessels crammed with migrants were sent back to sea despite a UN call to rescue thousands adrift in Southeast Asian waters with dwindling supplies of food and water.

About 2,500 migrants have landed on Indonesia's western tip and the northwest coast of Malaysia over the past week.

But two boats that crossed the Malacca Strait from the Thailand-Malaysia side have been turned away by the Indonesian navy, and on May 15 another was towed out to sea by the Thai navy.

Malaysia, too, has said it would push migrant boats back to sea.

"They have no food, no water and are drinking their own urine," said Joe Lowry, a spokesman for the International Organization for Migration in Bangkok.

“This is a game of maritime ping-pong with human life. We expect governments in the region to find a solution rapidly ... or we will be finding boatloads of desiccated corpses floating around in the Andaman Sea in coming days."

The crisis has arisen because smugglers have abandoned boats full of migrants, many of them hungry and sick, in the Andaman Sea following a Thai crackdown on human trafficking.

Thailand is the first stop on the most common trafficking route used by criminals preying on Rohingya as well as Bangladeshis seeking to escape poverty.

As some countries faced pressure for closing their doors to desperate "boat people", the U.N. human rights chief said the deadly pattern of migration by sea across the Bay of Bengal would continue unless Myanmar itself ends discrimination.

"Until the Myanmar government addresses the institutional discrimination against the Rohingya population, including equal access to citizenship, this precarious migration will continue," Zeid Ra'ad Al Hussein said.

Around dawn on Friday a boat with almost 800 people was brought ashore by fishermen along the coast of Aceh, on Indonesia's western tip, said Khairul Nova, a search and rescue official in the nearest town, Langsa.

"What I have been told by some of the people who were on the boat is that the boat was sinking and fighting broke out on board," Nova said. "We have seen many with injuries to the face and head. I don't know why (the fighting) happened."

However, in the same waters, the Indonesian navy pushed another boat back and Thailand's navy towed a wooden vessel with hundreds, including children, on board back out to sea.

"Those on the boat did not want to come to Thailand so we gave them food, medicine, fuel and water," said Thai Lieutenant Commander Veerapong Nakprasit. "This is not a push-back because these people wanted to go."

Veerapong said the boat was without a captain but that some of those on board had been trained by local Thai fishermen for a few hours to navigate.

The boat headed towards Indonesia early on Friday but had since looped back towards Malaysia, said Veerapong, who was monitoring the vessel's movements by radar.

"It's a cycle," he said. "It will keep on going."

The United Nations this week urged governments to fulfill an obligation to rescue those at sea and "keep their borders and ports open ... to help the vulnerable people who are in need".

However, there have been few signs that Southeast Asian nations are collaborating to avert a humanitarian crisis, in contrast with Europe, where countries are working together to deal with a tide of migrants crossing the Mediterranean.

Thai Prime Minister Prayuth Chan-ocha, whose government has announced a regional meeting on the crisis for May 29, said his country did not have the resources to look after the migrants.

"As there are many of them, we cannot look after them properly. Where will we put them?" Prayuth told reporters.

"Right now we have to find a place for them to stay. In the future, if many more of them come, it will cause a problem. They will steal the jobs and livelihoods of Thais."

Indonesia wanted to keep the boats out of its waters to dissuade more from coming, said military chief General Moeldoko.

"We will try to prevent them from entering our territory otherwise it will create social issues," Moeldoko told reporters after meeting President Joko Widodo in the capital Jakarta. "If we open up access, there will be an exodus here."

The United States last year downgraded Thailand and Malaysia to its list of the world's worst centres of human trafficking, dumping them in the same category as North Korea and Syria.