Democratic front-runner John Kerry racked up another win Tuesday night, but rival John Edwards finished a surprisingly close second in the Wisconsin primary.

The result means Kerry has, so far, won 15 of 17 state electoral contests.

As polls across Wisconsin began reporting Monday, Kerry and Edwards appeared to be running almost even in the race the for the state's Democratic presidential nomination. By late evening, Kerry had 39 per cent of the vote, and Edwards 35 per cent.

The two senators were surging far ahead of their nearest rival, former Vermont governor Howard Dean, who had 18 per cent with 83 per cent of polls reporting.

Associated Press reported that exit polls showed half of Wisconsin voters had made up their mind in the last few days. Many, it seems, ultimately favoured North Carolina's Edwards. According to exit polls, a great deal of his support came from Republicans and independents who plan to vote against the GOP in the fall.

Apparently heartened by his close second finish, Edwards told his supporters: "Objects in the mirror may be closer than they appear."

Democratic voters have been turning out in record numbers to cast ballots in the primaries, hoping to choose a candidate they believe can pose the strongest challenge to President George W. Bush in the November election.

But Edwards said the Wisconsin vote shows he has the support of the so-called independent voters crucial to winning the presidency.

And now that Dean's campaign seems doomed, Edwards says his campaign is gearing up.

"I've been looking forward to the time when this is a two-person race and people will focus on Senator Kerry and myself. It now appears we're very close to that place and may already be there," Edwards said.

"I think there are real differences between us and that's the moment I've been looking for."

In recent days, Edwards repeatedly criticized Kerry's support of the North American Free Trade Agreement -- an issue with some traction in a state most concerned with the economy and jobs.

Winless and running out of credibility, Dean is facing increasing pressure to cede the race. The early favourite had last week told supporters that a Wisconsin defeat would signal the end of his campaign.

But after the plea helped the former Vermont governor raise thousands, he abruptly changed his mind.

On Tuesday, Dean tried to put on a brave face. "We are not done yet together," he told supporters.

For his part, front-runner Kerry has postured as though the nomination race was over. Buoyed by his string of wins, Kerry ignored his rivals in Wisconsin, choosing instead to focus on President Bush.

The decorated Vietnam War hero has been portraying the Bush White House as a dangerous, far-right place pursuing an inept foreign policy.

In return, Republicans have portrayed the long-time legislator as a free-spending liberal bent on raising taxes and bloating government.

Hawaii, Idaho and Utah hold their votes on February 24. After that, candidates will be looking ahead to "Super Tuesday" on March 2, when California, New York, Ohio and seven other states award the delegates expected to make the choice for Democratic nominee unassailable.