Bangladeshi Prime Minister Sheikh Hasina has criticised economic migrants leaving the country calling them "mentally sick" and accusing them of hurting the country's image.

The state-run Bangladesh Sangbad Sangstha news agency quoted Hasina on Sunday as saying the migrants, many of whom are stranded in dire conditions at sea, had ample opportunities within the country.

"There is sufficient work for them, still they are leaving the country in such disastrous ways," Hasina said, adding the boat people were "mentally sick" for fleeing in search of jobs.

In her first comments on the migrant crisis in Southeast Asia, the prime minister said those leaving "could have better lives in Bangladesh".

Hasina said the migrants were "tainting" the country's image abroad and called on authorities to halt the flow of people leaving, and take action against human traffickers.

"Along with brokers, punishment will have to be given to those who are moving out of the country illegally," she was quoted as telling senior labour and employment ministry officials.

The region is currently battling an exodus of boat people fleeing persecution and poverty, with up to 2,000 vulnerable migrants thought to be stranded in the Bay of Bengal, many at the mercy of ruthless people smugglers.

Most are Muslim Rohingya from neighbouring Myanmar, where they are not recognised as citizens, but Bangladeshis trying to escape grinding poverty are also among the migrants.

More than 3,500 migrants have swum to shore or have been rescued off the coasts of Malaysia, Indonesia, Thailand and Bangladesh since the crisis erupted earlier this month.