KUALA LUMPUR, May 27 — No boats of Southeast Asian migrants have landed since the last one washed ashore in Indonesia a week ago.

Search and rescue vessels from Malaysia and Indonesia have found no more migrants at sea.

Some refugees appear to be returning to Myanmar.

While no one is willing to say definitively that there are no more boats out there, or to rule out a future exodus, the evidence suggests that the worst of the migration crisis that swept across Southeast Asia this month may have passed.

Just two weeks ago, thousands of migrants from Bangladesh and Myanmar, abandoned by smugglers and turned away by several countries, faced the prospect of dying at sea for lack of food and water.

Aid groups estimated that from 6,000 to 20,000 migrants were stranded in the Andaman Sea or the Malacca Strait, trapped in decrepit boats after the Thai authorities closed the deadly jungle camps that smugglers had used to detain the migrants to extract further payments before taking them to Malaysia.

One prominent aid worker, Chris Lewa, whose reports first brought international attention to the crisis, now says the number of migrants trapped at sea may have been 7,000 to 8,000, at the low end of her initial estimate.

“Maybe I was not that far off, and maybe there are no more boats left,” she said this week.

“People are asking me, how many are left at sea? I have no clue.”

About 3,500 migrants have arrived in Indonesia, Malaysia and Thailand in recent weeks, the International Organization for Migration says, with the last arriving last Wednesday.

Other migrants, many from Myanmar — members of the Rohingya ethnic group who had been fleeing persecution — may have returned there.

Rohingya in Myanmar have told Lewa’s group, the Arakan Project, that as many as 2,000 people who were held in boats off the Myanmar coast have now gone back ashore, paying the smugglers as much as US$300 (RM1,092) to smuggle them back in so that they could avoid being arrested for illegally re-entering Myanmar.

Myanmar’s government does not consider them citizens, rendering them effectively stateless.

On Monday, a US Navy P-8A Poseidon plane flying out of Subang, Malaysia, spotted one possible migrant boat in good condition with about 11 people visible on deck, a Defence Department official said, declining to give specifics such as the location of the vessel.

Lewa said her group had not received word of any departures from Myanmar since the beginning of May.

If the estimate of 7,000 to 8,000 was correct, that could still leave 2,000 or more migrants unaccounted for.

But officials from the Malaysian and Indonesian offices of the United Nations High Commissioner for Refugees stress that no one knows how many migrants, if any, remain at sea.

“I’m a bit surprised that those numbers haven’t actually been found,” Richard Towle, the refugee agency’s representative in Malaysia, said in a telephone interview Monday from Kuala Lumpur.

“We estimate that there are still groups out there, but it’s difficult to hazard any guess on the numbers.

“That’s longhand for saying we don’t know.”

Even if the immediate crisis has subsided, the underlying problems that caused it have not.

About 1 million Rohingya live in Myanmar, where they face discrimination and marginalisation.

And experts say the human smugglers who abandoned their quarry at sea after Thailand cracked down on their operations are likely to return to their trade as long as there is demand. — New York Times