About 13 000 boat people, including many stateless Rohingya Muslims, fled Myanmar and neighbouring Bangladesh in 2012 with hundreds dying during the perilous sea voyage, the UN said on Friday.
A wave of deadly sectarian violence in Myanmar's western state of Rakhine has triggered an exodus of refugees, mostly heading for Malaysia.
“We know of at least 485 people who've drowned or are lost at sea,” said Vivian Tan, spokeswoman for the UN refugee agency, adding the real death toll was probably far higher.
“These numbers are very worrying,” Tan said.
“The fact that even women and children are increasingly risking this journey shows the growing sense of desperation among the Rohingya in Myanmar and Bangladesh,” she added.
More than 10 000 people have attempted the sea voyage since October 2012 - a sharp increase on last season's departures, according to the Arakan Project, which lobbies for the rights of the Rohingya, said by the UN to be one of the most persecuted minority groups on the planet.
October is the end of the monsoon season and traditionally marks the start of an annual wave of migration by people trying to reach Malaysia from the Bay of Bengal - often on rickety wooden boats.
Myanmar views the roughly 800 000 Rohingya in Rakhine as illegal Bangladeshi immigrants and denies them citizenship. Thousands more live in squalid refugee camps across the border in Bangladesh.
Malaysia has become the sole hope for many Rohingya refugees, after Bangladesh closed its shared border to them and Thailand as well as Singapore refused to provide asylum to members of the Muslim-minority group.
Kuala Lumpur expressed concern at the influx of refugees, saying Malaysia's patience was being tested.
“There is the humanitarian aspect,” Malaysian Foreign Minister Anifah Aman told AFP on Friday, citing the recent rescue of 40 shipwrecked Rohingya who were turned away by Singapore.
“But we cannot allow Malaysia to become a destination of choice,” he added, noting that the country was already sheltering about 80 000 Rohingya. - Sapa-AFP