makeshift houses. There are 30 people dead and many injured," said an interior ministry official.
The blaze broke out at about 4 pm local time at the Mae Surin camp in Mae Hong Son province and was extinguished about two hours later, she said.
It is believed to have been caused by people cooking.
"Most of the dead are women, elderly and children. Some 200 are wounded and hospitalised," a senior national intelligence official said.
The Thai government pledged an investigation into the fire at the camp, which houses roughly 3,700 refugees.
"I regret this incident and too many people died," Interior Minister Jarupong Ruaengsuwan told AFP. "The casualties should not be so high. I will investigate the cause of the fire."
Ten camps strung out along the Thai-Myanmar border house a total of about 130,000 people, who first began arriving in the 1980s.
Many of the refugees have fled conflict zones in ethnic areas of Myanmar, also known as Burma.
Families often live cheek-by-jowl in simple bamboo-and-thatch dwellings.
Many of the camp residents have been registered with the UN as refugees, and an ongoing resettlement programme has allowed tens of thousands to move to third countries.
After a new quasi-civilian government replaced the long-ruling junta in Myanmar two years ago, Thailand announced it wanted to shut the border camps, raising concern among their residents.
But so far the displaced residents have been allowed to stay and the Thai government has stressed that it will only send them back when it is safe.
Many of the refugees are from Myanmar's eastern Karen state, where a major rebel group, the Karen National Union (KNU) signed a ceasefire deal with the new regime last year after decades of civil war.
Vast numbers of people fled the former Myanmar junta's counter-insurgency campaign, which rights groups say deliberately targeted civilians, driving them from their homes, destroying villages and forcing them to work for the army.
Years of war have left the Karen region littered with landmines while development has been held back, leaving dilapidated infrastructure and threadbare education and health services.
Hundreds of homes were destroyed at a different border camp in February last year by a fire that the authorities also blamed on cooking.