With provisional results from more than half of the polling stations released by the electoral authority, 67 percent of Kenyans had backed the charter, making it extremely unlikely the "No" camp could catch up.

The "Yes" camp claimed victory late on Thursday morning with Energy Minister Kiraitu Murungi saying Kenyans had spoken with a "thunderous voice" and that "Kenya has been truly reborn."

Higher Education Minister William Ruto, leader of the "No" side, then conceded defeat but quickly went on the offensive before a news conference due to be held later by the winners, President Mwai Kibaki and Prime Minister Raila Odinga.

Ruto said 60 percent of registered voters had abstained or said "No," so there should be immediate consultations with the "Yes" side on agreeing amendments to the new draft.

Coming two years after allegations over vote-rigging in a presidential election ignited violence that killed 1,300 people, the referendum boosted the Kenyan shilling against the dollar and extended the Kenyan stock market's recent gains.

The changes put to voters on Wednesday allow for greater checks on presidential powers, more devolution to grassroots administrations and an increase in civil liberties.

The new legal framework addresses the corruption, political patronage, land-grabbing and tribalism which have plagued Kenya since it won independence from Britain in 1963.

"Confidence was a key requirement for economic turnaround, and the peaceful passage of the vote should do a lot to underscore that," said Razia Khan, Africa economist at Standard Chartered Bank.