Hillary Clinton has given her campaign a much-needed boost after winning the Pennsylvania primary for the Democrats.

Reports indicate that Clinton's victory over Barack Obama was aided by white working class voters and women.

With 90 per cent of the vote counted so far, reports indicate the New York senator has 55 per cent of the vote, while Obama, the rookie senator from Illinois, has won 45 per cent.

"Some counted me out and said to drop out," Clinton told supporters. "But the American people don't quit. And they deserve a president who doesn't quit, either."

Obama had said he was "not predicting a win" for himself.

"We think we've made enormous progress," Obama said Tuesday in Pittsburgh.

Obama had predicted that Tuesday's results would be close and that he was going to do a lot better than people expected. He had outspent Clinton by about two-to-one in the state. But Clinton was seen as having an organizational edge.

Early results and exit polls also show that the Democratic primary may have doubled its turnout from the last presidential election in 2004. As many as two million voters may have cast their votes.

During the past six weeks, both Clinton and Obama have battled hard for the state in a campaign that had turned increasingly hard-edged.

Analysts said Tuesday night that Clinton needed to win big -- by double digits -- if she hopes to turn the tide in her fight with Obama.

Late polling showed Clinton holding a single-digit lead in Pennsylvania, a drop from the 20 points or more she held over Obama in earlier surveys. On voting day, Clinton lowered expectations about her potential victory.

The party's nomination will be determined by delegates, some of whom are determined by voters in the primaries and others who have been selected by the party. Whichever candidate is able to secure 2,025 delegates will win the nomination.

Before Tuesday's results, Obama had 1,645 delegates and Clinton had 1,507, according to The Associated Press. But neither candidate is expected to reach the 2,025 delegates needed to secure the Democratic nomination without the support of superdelegates, a group of about 800 party insiders.

Obama -- who is ahead in fundraising, delegates, the popular vote, and states won this primary season -- doesn't necessarily need to win Tuesday to eventually secure the nomination.

"If this is close, very close, or if Barack wins, it is over... for Hillary Clinton," Democratic consultant Peter Fenn said Tuesday.

United Steelworkers President Leo Gerard, a Canadian who can't vote in the U.S. election, said his 175,000-strong membership in Pennsylvania is "equally divided" between Clinton and Obama.

"There's a lot of our members who think Hillary Clinton has a lot of experience," Gerard told CTV's Canada AM on Tuesday. "But there's also a tremendous amount of our membership that think Barack's message of hope and his message of change and his attraction to young people could be a turning point in this election."

Gerard said he is meeting with members of the union's board on Wednesday to decide if his union will endorse either candidate or if they'll wait until the North Carolina primary.

Delegate count

About four million Democrats are eligible to cast ballots in Pennsylvania, with 158 delegates at stake. Some Democrats say they are concerned about a prolonged race between their two candidates. The race in Pennsylvania has become increasingly negative in the past few weeks.

In television ads released Monday, each candidate questioned the credibility of their rival.

Clinton's ad showed images of the 1941 attack on Pearl Harbor and Osama bin Laden. It then featured a quote by Harry Truman -- the U.S. president who dropped two nuclear bombs in the closing days of World War II -- who said, "If you can't stand the heat, get out of the kitchen."

The Obama campaign accused Clinton of appealing to people's fears.

Hours later, the Obama campaign aired a response ad challenging Clinton's 2002 vote authorizing the U.S. invasion of Iraq.

With files from The Associated Press