Hundreds of people including many children have fled a flare-up in fighting between the Myanmar army and an ethnic minority insurgent group, taking refuge across the border in Thailand, Thai authorities and an aid worker said.

About 700 people had fled to the Thai town of Mae Sot after fighting between the Karen National Union (KNU) and Myanmar's army, authorities in the western Thai border province of Tak said in a statement.

Ye Min, an official at the...