All the boats appear to have been abandoned as Thailand, their usual destination, cracks down on the trafficking of ethnic Rohingya Muslims bound for neighbouring countries, after the discovery of dozens of remains in mass graves at "slave camps" in the Thai south, a PTI news report said.

More than 1,000 migrants from Bangladesh and Myanmar landed in Malaysia after being dumped by human traffickers in shallow waters off the resort island of Langkawi, police said.

"We think there were three boats that ferried 1,018 migrants," said Langkawi Deputy Police Chief Jamil Ahmed, adding that the number was expected to grow as more migrants are picked up around the island.

In the early hours of today, Indonesian search and rescue teams discovered another boat drifting off east Aceh with 400 men, women and children from Myanmar and Bangladesh aboard, Aceh provincial search and rescue chief Budiawan told AFP.

Authorities are bracing for further arrivals and have recruited fishermen to assist in patrolling the coast of the remote western Indonesian province.

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

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.

Thousands have braved the dangerous sea crossing from Myanmar to southern Thailand and beyond in the hope of reaching mainly Muslim Malaysia, but many often fall prey to people-traffickers in Thailand.

Chris Lewa from The Arakan Project, a Rohingya rights group, said she believes thousands of migrants are trapped at sea following crackdowns on trafficking in Thailand as well as in Malaysia in recent months.