At least 15 Rohingya refugees have died and dozens more are unaccounted for after their overcrowded wooden boat heading for Malaysia sank off the coast of southern Bangladesh, officials have said.

Some 130 people - mainly women and children - were packed on the fishing trawler that was trying to get across the Bay of Bengal to Malaysia, coastguard spokesman Hamidul Islam told the AFP news agency on Tuesday. Seventy people had so far been rescued.

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The International Organization for Migration (IOM) and the UN refugee agency issued a joint statement saying they were ready to support the survivors of the boat.

"UNHCR and IOM are saddened by this tragic loss of life and, together with our other UN and NGO partners, are standing by to offer assistance to the [Bangladeshi] government in responding to the needs of the survivors, be it food, shelter, or medical aid."

Many of the nearly one million Rohingya, who have taken shelter in overcrowded refugee camps in Bangladesh's Cox's Bazar district, have tried to go to Malaysia by boat.

The boat, barely 13 metres (40 feet) long, was one of two vessels attempting the hazardous 2,000-kilometre (1,250-mile) journey before the monsoon season starts.

Four navy and coastguard boats were searching the seas near St Martin's island, officials said.

"We have found one capsized boat. All of them were mainly from the refugee camps in Cox's Bazar. We haven't found any sign of the second boat yet. We will continue our operation," Islam said.

Those on the boat were hoping to reach Malaysia and were being aided by traffickers, Noor Ahmed, the top elected official on the island, told The Associated Press news agency, quoting accounts by the survivors.

Risky trips

More than one million Rohingya refugees, 700,000 of whom fled a brutal military crackdown in Myanmar in 2017, currently live in camps in Bangladesh.

Malaysia is the favoured destination of the Rohingya as it is a Muslim majority nation and has a sizeable Rohingya diaspora.

With few opportunities for jobs and education in the camps, thousands have attempted to reach other countries in Southeast Asia.

Since last year, Bangladesh's law enforcement agencies have picked up more than 500 Rohingya from coastal villages and boats as they waited to board boats.

At least seven suspected traffickers were shot dead in 2019 in clashes with police.

Trafficking often increases during the November-March period when the sea is safest for the small fishing trawlers used in the risky trips.

An estimated 25,000 Rohingya left Bangladesh and Myanmar on boats in 2015 trying to get to Thailand, Malaysia and Indonesia. Hundreds drowned as overloaded boats sank.