At least 15,000 refugees have fled Burma to Thailand as ethnic rebels and Burmese government troops clashed Monday after the country's first general election in 20 years.

Burmese citizens gather while waiting for food at the Border Patrol Police base in the Thai town of Mae Sot. Fighting between Burmese soldiers and ethnic Karen fighters came a day after the country's first election in two decades. (Apichart Weerawong/Associated Press)

Thai officials told The Associated Press that the main fighting involving Karen fighters occurred in the border town of Myawaddy in Burma, also known as Myanmar. At least 10 people were wounded in the fighting that involved gunshots and mortar fire, the news agency reported.

More fighting broke out further south at the Three Pagodas Pass, but there was no word on casualties.

Groups from Burma's ethnic minorities, who make up about 40 per cent of the population, had warned in recent days that civil war could erupt if the military tried to impose its highly centralized constitution and deprive them of rights.

The UN was helping to care for the refugees being sheltered at a makeshift camp near the border.

"As soon as the situation is under control, we will start sending the refugees back to Myawaddy," said Thai army Col. Wannatip Wongwahe.

Canadian on scene says exodus a surprise

Justin Klassen, a Canadian who lives in the Thai city Mae Sot just across the border from Myawaddy, said the refugees are jammed into a space the size of three or four football fields at a nearby airbase.

Burmese citizens cross the Moei River into Thailand as they flee Myawaddy following fighting between ethnic rebels and government troops. (Apichart Weerawong/Associated Press)There is a shortage of food, water and blankets and relief agencies are scrambling to deal with the mass exodus, which came as a complete surprise, Klassen said in an email.

While news agencies have estimated the number of refugees at about 15,000, Klassen said he believes the figure had ballooned as high as 30,000 by nightfall.

Klassen, 24, who is from Niagara Falls, Ont., has been working as a volunteer in the Thailand-Burma border area since June assisting refugees with issues such as political asylum and human trafficking, his family said.

Early election results suggested that parties linked to the military regime, which has ruled Burma for 48 years, were winning.

As votes continue to be counted, state media and the Election Commission reported that 40 junta-backed candidates had already won.

The vote, boycotted by the main opposition National League for Democracy, has been condemned by a number of Western leaders.

Obama says vote 'neither free nor fair'

U.S. President Barack Obama, on a visit to neighbouring India, called the vote "neither free nor fair."

Speaking to India's parliament Monday, Obama said it was unacceptable for Burma's government to "steal an election" and hold its people's aspirations hostage to the regime's greed and paranoia.

Independent candidates say they faced obstacles to registering and campaigning. Many opposition parties faced expensive registration fees, which prevented them from fielding candidates, and many potential opposition candidates found themselves under arrest in the months leading up to the vote.

Foreign journalists and independent election monitors were barred from the country. The BBC managed to get a reporter into the country, but for security reasons was not releasing that person's name.

The two main parties in the vote are closely aligned with the country's military junta.

The Union Solidarity and Development Party, which has the backing of the military government and is widely expected to emerge as the winner, fielded 1,112 candidates for the 1,159 seats in the two-house national parliament and 14 regional parliaments.

The USDP's main rival, the National Unity Party, was running 995 candidates. The National Unity Party is backed by supporters of Burma's previous military ruler.

The third biggest party, the National Democratic Force, formed by breakaway members of Aung San Suu Kyi's party, fielded just 164 candidates, including 141 in the national parliament. It is the main standard-bearer for the broadly defined pro-democracy movement.

With files from The Associated Press