Malaysian patrols searched coastal waters in the Andaman Sea on Monday for dozens of members of Myanmar's Rohingya ethnic group, after a boat believed to be carrying them sank last week and another went missing.
At least 21 bodies have been found since the vessel went down on Thursday - 12 in Malaysia and nine in neighbouring Thailand - the regional head of Malaysia's maritime agency, Romli Mustafa, told reporters.
Without life jackets, it might be difficult for many to survive even 24 hours, but some could be holding on to floating objects and search operations would continue, he added.
"Weather conditions are not so friendly but anyhow, we're trying our level best," Romli said. So far, 13 survivors had been rescued, he added.
Hundreds of Rohingya people boarded a vessel bound for Malaysia two weeks ago, and were transferred onto two boats on Thursday, according to Khairul Azhar Nuruddin, Police Chief on Malaysia's northern Langkawi island, the centre of search operations.
The smaller ship carrying around 70 people sank near Langkawi the same day and the fate of the other boat carrying 230 passengers remains unclear, Malaysian authorities said.
In the last week of October, multiple boats carrying Rohingya left Cox's Bazar in Bangladesh, said Chris Lewa, director of the non-profit Arakan Project, which tracks the voyages.
It typically takes a week to 10 days to reach Malaysian waters, Lewa told Reuters. The boats might also have stopped in waters off Myanmar to pick up Rohingya coming from inland areas of Rakhine state.
More than 5,100 Rohingya boarded boats to leave Myanmar and Bangladesh between January and early November this year, and nearly 600 of them have been reported dead or missing, according to data from the UN Refugee Agency.
Muslim-majority Malaysia has long been a favoured destination for Rohingya fleeing persecution, although the country does not recognise refugee status. In recent years, it has turned away boats and detained Rohingya as part of a crackdown on illegal migrants.
Malaysian police said on Monday those rescued had been detained pending an investigation into potential immigration offences.
Thailand and Malaysia have deployed air and sea patrols in a search operation that could last a week, Malaysian maritime official Romli said.
Information received by the agency indicated that the first boat the Rohingya boarded had left from Rakhine state, which borders Cox's Bazar in Bangladesh where the sprawling refugee camps are located, Romli added.
In Thailand, authorities recovered refugee cards issued in Bangladesh from two children which identified them as Rohingya living in the Cox's Bazar camps, according to the Thai official.
(Reporting by Huey Mun Leong in Langkawi, Malaysia, Ruma Paul in Dhaka, Bangladesh and Panarat Thepgumpanat in Bangkok; Additional reporting by Rozanna Latiff in Kuala Lumpur; Writing by Martin Petty and Devjyot Ghoshal; Editing by David Stanway, Kate Mayberry and Andrew Heavens)