Malaysia has denied entry to a boat carrying about 200 Rohingya due to coronavirus fears, the air force said, after news emerged this week that scores died on another crowded vessel.

Activists are now fearful that large numbers of Rohingya, a persecuted Muslim minority from mostly Buddhist Myanmar, may be trapped on boats at sea and unable to reach other countries.

The latest developments have sparked concerns of a repeat of a 2015 crisis when many Rohingya died at sea after Southeast Asian nations turned their boats back following the collapse of long-established people smuggling routes.

In the latest incident, the Rohingya boat was spotted Thursday by a Malaysian air force jet off the northwestern island of Langkawi and then intercepted by two navy vessels backed by a helicopter.

Malaysian sailors gave the Rohingya food before escorting them out of the country's waters, the air force said.

"With their poor settlements and living conditions... it is strongly feared that undocumented migrants who try to enter Malaysia either by land or sea will bring (COVID-19) into the country," said an air force statement late Thursday.

It added that "maritime surveillance operations will be intensified".

The development signalled that Malaysia, which is under a nationwide lockdown to combat the spread of the virus after recording more than 5,000 cases and 80 deaths, is toughening its stance to deny Rohingya entry.

While relatively few boats carrying the minority have arrived in Malaysia since the 2015 crisis, some have been allowed into the country. Earlier this month, 202 Rohingya landed in Langkawi and were detained.

'Death sentence'

Malaysia is a favoured destination for the migrants from Myanmar as it is a Muslim-majority nation with a sizeable Rohingya diaspora.

Many travel on crowded, rickety boats from squalid camps near Bangladesh's border, home to nearly a million Rohingya who fled Myanmar after a military offensive in 2017.

In the earlier incident, 60 Rohingya died on a boat crammed with hundreds of people stranded in the Bay of Bengal for more than two months, according to survivors.

That vessel was denied entry by Malaysia and Thailand and then headed back to Bangladesh where the migrants were picked up by the coast guard late Wednesday. About 400 people were rescued.

Activist group Fortify Rights said Rohingya had told them other ships were adrift at sea between Bangladesh and Malaysia, and urged regional governments to allow boats ashore.

"Sending an ill-equipped ship of refugees out to sea is unlawful and a death sentence," said the group's CEO Matthew Smith.