Thousands have fled across the Burmese border to escape clashes between troops and ethnic Karen rebels, a day after the first election in 20 years.
Thai officials said more than 10,000 people had fled the fierce fighting in and around the town of Myawaddy.
It erupted on Sunday in a protest linked to the election.
The poll, which was boycotted by the main opposition group, was marred by campaign restrictions, reports of irregularities and low turnout.
Votes are still being counted, but two parties closely linked to the ruling military junta are expected to do well.
The poll is the first in Burma since 1990, when the Aung San Suu Kyi-led National League for Democracy secured an overwhelming victory but was never allowed to take power.
The ruling generals say the election marks the transition from military rule to a civilian democracy, but the poll has been widely condemned as a sham. Western governments say it was neither free nor fair.
Despite this, some analysts say the election - although deeply flawed - could mark the start of a process of democratisation, by giving opposition lawmakers a voice, however limited, in the institutional decision-making process.
BBC News
