Southeast Asian countries were urged on Tuesday to treat migrants landing on their shores humanely and avoid a repeat of this year's disaster in which hundreds of refugees were either lost at sea or died in jungle camps.

The International Organization for Migration (IOM) called for "full cooperation" this week from governments attending a Bangkok meeting in May aimed at tackling the region's annual migrant crisis as European countries struggle to cope with refugees fleeing war in Syria and Iraq.

Southeast Asian nations agreed to help vulnerable "boat people" stranded at sea following last year's crisis that saw more than 4,000 migrants land in Indonesia, Malaysia, Thailand, Myanmar and Bangladesh following a Thai crackdown on people-smuggling gangs.

Some were trapped on boats in the Bay of Bengal and Andaman sea. Hundreds drowned.

October and November mark the start of the four-month "sailing season", the busiest time for smuggling and trafficking ships plying the Bay of Bengal.

"We are still calling for safe disembarkation and humanitarian treatment - shelter, hydration, medical care and safety from the elements and criminality - and full cooperation from all actors, from the international community, that lives are not lost," Joe Lowry, the IOM's spokesman in Asia-Pacific, told Reuters.

Thousands of migrants have fled persecution and poverty in Myanmar and Bangladesh. Many of them are members of Myanmar's Rohingya Muslim minority who live in apartheid-like conditions in the country's Rakhine state, paying smugglers to board rickety boats to sail across to Malaysia.

Some ended up in the hands of traffickers and were held near Thailand's border with Malaysia in often brutal and filthy conditions for months or even years until they could pay a ransom for their release.

A clamp-down by Thai police on human trafficking gangs triggered the regional crisis earlier this year. It followed the discovery in May of 30 bodies in graves near the Thai-Malaysian border, which sparked international outcry.

Thailand has charged 88 people suspected of involvement in human trafficking since launching the investigation into gangs but scores more are on the run.

In Foreign Ministry letter to international organisations dated Nov 23, the ministry said a migration meeting to be held on Friday was "Thailand's proactive step to pre-empt any possible recurrence of humanitarian crises of May 2015".

Thailand's Interpol director, Pol Maj Gen Apichart Suribunya, told Reuters ships were bypassing Thailand and heading directly to Malaysia following the Thai crackdown.

"Malaysia is having a headache," he said.

Since late September, when monsoon conditions began to subside, several boats have smuggled a total of about 1,000 passengers across the Bay of Bengal, according to the U.N. refugee agency and the migration-tracking group Arakan Project.

Lowry of IOM said migration patterns had changed.

"The obvious thing is people go directly to Malaysia which cuts out potential for profit for smugglers," he said.