A major mudslide at a tea plantation in Sri Lanka killed about 100 people on Wednesday, with the victims buried alive, the country's disaster management minister said.

"I went to the spot. What I gathered is that about 100 people have been buried alive," Disaster Management Minister Mahinda Amaraweera told AFP by telephone after visiting the site in the eastern Koslanda region.

"There is no chance they could have survived."

The minister said that the search and rescue mission led by troops had now turned into a recovery operation, which they hope to resume at first light on Thursday.

He said using heavy machinery had to be done carefully because the surrounding hills were unstable.

"Initially we estimated the missing number at 300, but most of them were at school or work," the minister said.

"We have already started relief operations to provide them with shelter and food."

"Even the office where records were kept had been damaged," the minister said.

The region's top military official Major General Mano Perera said 302 people, including 75 school children, whose homes were destroyed in the mudslide were being looked after at two schools in the area.

The mudslide hit at a time when most people were at work and children were already in school, leaving the elderly and the very young at home.

The military officer said about 500 troops had been deployed in the area to carry out the search for victims.