The party allied to ousted and exiled ex-leader Thaksin Shinawatra has won a major victory in Thailand's general election, BBC reported, citing provisional results.

With most votes counted, outgoing Prime Minister Abhisit Vejjajiva has conceded victory to his rival, opposition leader Yingluck Shinawatra.

Tingluck, who will become Thailand's first female prime minister, said there was "a lot of hard work ahead".

She is the younger sister of Thaksin Shinawatra, ousted in a coup in 2006.

With 92% of votes counted, Yingluck's Pheu Thai party had won 260 seats, giving it a majority in the 500-seat parliament.

"It is now clear from the election results so far that the Pheu Thai party has won the election, and the Democrat Party concedes defeat," Abhisit said on national TV.

"I will give the chance to Yingluck, the first woman to form a government," he added. "I want to see unity and reconciliation. The Democrats are ready to be in opposition."

After Abhisit admitted defeat, Yingluck was cautious in her response. She thanked Mr Abhisit and said she would wait for the official results to be declared.

"I don't want to say it is victory for me and the Pheu Thai party but people are giving me a chance and I will work to my best ability for the people," she said at her party headquarters.

"I would like to reiterate that we are ready to deliver on all of the policies that we have announced. There is a lot of hard work ahead."

She said her party officials had been in talks with the smaller Chart Thai Pattana party with a view to forming a coalition.

"In the future there are more parties expected to come and work with Pheu Thai," she said.