The leafy London commuter belt of Chislehurst is the kind of traditionally Conservative supporting suburb that Boris Johnson must win to seize the mayoralty from incumbent Ken Livingstone.

Conservative candidate Johnson has been campaigning hard in London's "outer doughnut" to bring out support that stayed away from his party in the last two mayoral elections in 2000 and 2004.

One-time socialist firebrand Livingstone won both elections by comfortable margins but this time round opinion polls have put both candidates neck and neck, with old Etonian Johnson marginally ahead.

The final result will not be declared till Friday evening, but Johnson's outer London efforts appeared to be paying off on voting day in semi-rural Chislehurst on the capital's south-east edge on Thursday.

Most voters spoken to by Reuters said they had either voted for Johnson or against the Labour party's Livingstone.

Many who had previously voted for the mayor said they had switched allegiance to Johnson this time.

But support for Johnson was in many cases a reaction against Livingstone's eight-year term, with voters saying it was time for a change.

"I think two terms is long enough," said Paul Chapman, 40, a bank employee, who switched from Livingstone to Johnson.

"I think Livingstone has run out of ideas, we need a fresh face, a bit of a change."

Property manager Kevin O'Donnell, 47, voting in the mayoral elections for the first time, also plumped for Johnson.

"I'm fed up with Ken Livingstone," he said, adding that he feared that inner London's traffic congestion zone could be widened to the outer suburbs.

Backing for Johnson, a former editor of the right-wing Spectator magazine, was frequently less than full-hearted.

"I don't think he's the greatest candidate but I prefer him to Mr Livingstone," said retired accountant John Stanley, 77.

"Boris is an unknown," said retired marine seismologist Tony Morgan, 66, who also changed allegiance from Livingstone to Johnson. "Give him a chance, let him get on with it."

One lifelong Labour voter and former Livingstone supporter said she had abandoned him because of worries over the cost of the 2012 London Olympics and alleged corruption at City Hall.

The 56-year-old freelance business consultant, who requested anonymity, said she had voted for Liberal Democrat ex-policeman Brian Paddick instead because she would "have difficulty voting Conservative in any election".