About 3,000 villagers from Myanmar's southeastern Karen state fled to Thailand on Sunday following air attacks by the army, local media said.

Myanmar’s military launched air strikes on five areas near the border, including a displacement camp, the Karen Women’s Organization said.

"At the moment, villagers are hiding in the jungle as more than 3,000 crossed to Thailand to take refuge," a statement from the group said.

Thai PBS reported about 3,000 had reached Mae Hong Son.

At least two soldiers from the Karen National Union were killed, said David Eubank, founder of the Free Burma Rangers, a relief organisation.

"We haven’t had air strikes there for over 20 years," Eubank said. "Second, these were at night, so the capability of the Burma military has increased with the help of Russia and China and other nations, and that is deadly."

Myanmar army fighter jets launched air strikes on Saturday on a village near the Thai border in territory controlled by an armed ethnic group, the group said, as fears grow of civil war following last month's military coup.

"They bombed the area... The villagers from that area said two dead and two injured," a spokesperson for the Karen Peace Support Network said, adding that communication was difficult in the remote region and there could be more casualties.

A spokesman for the junta did not answer phone calls seeking comment.