"The operation is expected to take one day."
Sunai Phasuk, a consultant at the New York-based Human Rights Watch, told Al Jazeera that repatriation on the scale has not been seen before.
"It is very concerning that the Thai army has enforced a communications blackout in and around the camp. Mobile phone signals have been jammed for the past two days, and nobody knows what exactly is going on or whether force has been used to move the Hmong onto the buses," he said.
The Hmong refugees are seeking asylum in Thailand saying that they face persecution from the Laotian government for fighting alongside US forces during the Vietnam War.
Known as America's "forgotten allies", the ethnic group from the remote mountains in Laos were recruited by the US Central Intelligence Agency to fight alongside US forces during the Vietnam War.
|Thai soldiers have been deployed to move refugees from the camp [AFP]
Over 300,000 Laotians, mostly Hmong, fled to Thailand after the Pathet Lao communists took power in 1975, citing political persecution.
Most were resettled in third countries with many now living in the US.
Thai officials say the group at the Huay Nam Khao camp are economic immigrants who entered the country illegally.
They have refused to grant the UN Refugee Agency access to the camp to assess whether any are political refugees.
But the deportations have been criticised by the human rights groups and the US, which has said it would be "deeply dismayed" by any move to force the refugees back to Laos.
"We have made it abundantly clear that we are prepared to roll up our sleeves and work with partners in Thailand for a solution that is humane and responsible," Eric P. Schwartz, the US assistant secretary of state for population, refugees and migration told the AFP news agency on Sunday.
"Even at this late date we're fully prepared to do that," he said.
Last week Antonio Guterres, the head of the UN refugee agency, urged Thailand to call off the expulsions, saying they would "set a very grave international example".
The Thai government has promised Laos, which insists the group will be safe after returning, that they would be sent back by the end of the year.
"The Lao government confirmed that they will give amnesty to the Hmong leaders," Thana said on Monday.