At least 20 people were killed when a boat carrying scores of wedding guests capsized in Myanmar's Irrawaddy Delta, officials said, with more feared drowned as rescue workers renewed their search in daylight.

Most of the dead were women, according to officials, who said the boat sank on Friday evening when it collided with a river barge in Pathein, a port city west of the commercial capital Yangon.

"Altogether 16 women and four men were killed in the boat accident," regional MP Aung Thu Htwe told AFP on Saturday morning.

"We estimate nine people are still missing," he said, adding that some 30 people had been rescued alive the night before.

The boat was believed to be carrying between 60 and 80 people when it sank, according to state media and a local police officer.

"They were crossing to the other side of the river after attending a wedding in Pathein. Most of them were relatives from the same village," said the police officer, who requested anonymity.

Both boats were unlit when they collided in the middle of the river, he added.

Local authorities and Red Cross workers resumed the search operation this morning, the police officer said.

"We will do search and rescue for the whole day," he told AFP.

Fatal boat accidents are common in Myanmar, where many people living along its flood-prone rivers rely on often overcrowded ferries for transport.

In October, 73 people, including many teachers and students, died when their packed vessel capsized in central Myanmar on the Chindwin River.

Earlier that year in April at least 21 people, including nine children, died after their boat sank off the coast of Myanmar's western state of Rakhine.

Around 60 people died the year before, in March 2015, when their ferry went down in the same treacherous waters off the Rakhine coast.