Myanmar's navy seized a boat packed with 727 people off the country's southern coast on Friday, the government said, about a week after it found a similar boat it said carried around 200 Bangladeshi migrants.

The nationality of the people on the boat was unclear. Myanmar's Ministry of Information described them as "Bengalis", using the term the government uses to describe the country's persecuted Muslim Rohingya minority as well as immigrants from Bangladesh.

Myanmar insisted it was not to blame for Southeast Asia's latest influx of "boat people" at a regional crisis meeting in Thailand on Friday, as the United States said thousands of vulnerable migrants remained adrift at sea and needed urgent rescue.

More than 3,000 migrants have landed in Indonesia and Malaysia since Thailand launched a crackdown on human trafficking gangs this month. About 2,600 are believed to be still adrift.

"Myanmar navy is now transporting the boat to its base on Hainggyi Island," said Tun Kyaw Kyaw, the Deputy Director General of the Ayeyarwady Division government, responsible for the area region where navy base is located.

The island is also on Myanmar's southern coast, close to the place where the boat was seized.

"After sending the people to the island, we will investigate them," said Tun Kyaw Kyaw, adding that the examination was necessary to determine their identity.

Pictures posted on the Ministry of Information's Facebook page showed scores of men huddling shoulder-to-shoulder under the sun on the front deck, while uniformed officials - one of them carrying a rifle - stood above. Women could be seen crammed together in the boat's cabins.

The navy found the boat 30 nautical miles off Myanmar's southern coast in the Andaman Sea. The government said there were 608 men, 74 women and 45 children on board.