KUALA LUMPUR (AFP) - Nearly 2,000 boat people from Myanmar and Bangladesh have been rescued or swum to shore in Malaysia and Indonesia, the authorities said on Monday, warning that still more desperate migrants could be in peril at sea.

The spate of arrivals comes as Thailand, their usual destination, cracks down following the discovery of mass graves that has laid bare the extent of a thriving human-smuggling ring in Southeast Asia.

Thousands of impoverished Muslim Rohingya - a minority unwanted by Myanmar's government - and Bangladeshis have been braving a perilous sea and land trafficking route through Thailand and into Malaysia, Indonesia and beyond every year.

Malaysian police said people-smugglers had dumped more than 1,000 hungry migrants in shallow waters off the coast of the resort island of Langkawi since Sunday. "We think there were three boats that ferried 1,018 migrants," said Langkawi deputy police chief Jamil Ahmed.

He added that one boat was confiscated but the others are believed to have fled to sea. Jamil said more of the castaways were expected to emerge from the island.

In Indonesia, a boat was found off the far west coast early Monday with more than 400 people aboard, authorities said, a day after 573 people described by one official as "sad, tired and distressed" came to shore off the northwest province of Aceh.

At least 92 children were among those brought ashore in the two countries.

Aceh provincial search and rescue chief Budiawan, who like many Indonesians goes by one name, told AFP authorities were bracing for further arrivals and have recruited fishermen to assist in patrolling coastal areas.

"We are on standby and ready to rescue them when we receive an alert," Budiawan said.

Thai crackdown 'raises risks'

Activists and refugee groups say the Thai crackdown may be imperilling migrants already in the pipeline, leaving them stuck in appalling conditions with little or no food on overcrowded ships, or at risk of being dumped at sea by nervous smugglers.

"Thailand has tried to prevent traffickers from continuing their business... so that has forced them to go somewhere else," said Chris Lewa from The Arakan Project, a Rohingya rights group, who believes thousands may be at sea. Migrants are "just trying to disembark before they die", she added.

Buddhist-majority Myanmar views its population of roughly 800,000 Rohingya as illegal Bangladeshi immigrants, and they have been targeted in outbreaks of sectarian violence there in recent years, prompting many to flee. Boatloads of Rohingya have arrived off Aceh in the past, typically after becoming lost or running out of fuel.

One passenger who straggled ashore in Aceh on Sunday told local journalists their vessel had set out from Thailand for Malaysia.

Indonesian officials said the passengers were tricked and told to swim to land. "One of the migrants who could speak Malay told me that their agent had told them they were in Malaysia, and to swim to shore," Darsa, a local disaster management agency official, told AFP.

Darsa said the passengers included 83 women and 41 children. One woman was pregnant and some of the children were aged under 10.

"Some of them were not doing too well and needed medical attention," he said.

Jamil, the Langkawi police official, said the 1,018 people found there included 555 Bangladeshis. There were 463 Rohingya, including 101 women and 52 children. All appeared to be in decent health, he said.

Both Malaysia and Indonesia were feeding and providing medical care to the migrants until their legal or refugee status can be determined.

The UN considers the Rohingya to be one of the world's most persecuted minorities.

Thai authorities have been at pains to show they are serious about tackling people-smuggling after years of accusations that they turn a blind eye to - or are even complicit in - the trade.

Four secret jungle camps have now been found in southern Songkhla province since last weekend, as well as 33 bodies in various states of decay, Thai police have said, with many pulled from shallow graves.

The discovery has raised fears that similar camps could exist in Malaysia along its Thai border. But Home Ministry secretary-general Alwi Ibrahim said on Sunday that there were no such camps on Malaysian soil, a view supported by Rohingya activists in the country.