WASHINGTON -- New Jersey Gov. Chris Christie, a possible Republican presidential candidate, was easily re-elected in one of the key races in the United States' off-year elections. Republicans narrowly lost the governor's seat in Virginia, while New Yorkers elected a liberal Democrat to succeed billionaire Michael Bloomberg as mayor.

His landslide victory on Tuesday in a Democratic-leaning state demonstrated Christie's broad, bipartisan appeal and could boost his candidacy should he seek the presidential nomination in 2016.

The off-year vote will be scrutinized for clues to the mood of Americans ahead of next year's congressional elections -- especially with a pragmatic conservative Republican, Christie, prevailing in New Jersey, while a more ideological one, Ken Cuccinelli, lost in Virginia. But the answers could be murky. Both races were shaped by the personalities and issues in those states and it could be hard to judge if there are national implications. And the Virginia race, won by Democratic businessman Terry McAuliffe, turned out much tighter than polls had anticipated.

New Yorkers elected Bill de Blasio, head of the city's public watchdog agency, to replace Bloomberg, the Republican-turned-independent who has been the city's mayor for 12 years. Though New York is overwhelmingly Democratic, it hasn't had a Democratic mayor in 20 years, after Bloomberg's three terms and two by his Republican predecessor, Rudolph Giuliani.

In other, widely scattered balloting, Colorado voters agreed to tax marijuana at 25 per cent with the proceeds dedicated to regulating the newly legalized drug and building schools. In Washington state, a ballot measure requiring mandatory labeling of genetically modified food was failing in early returns.

Alabama Republicans chose the establishment-backed Bradley Byrne over a rival tea party-supported rival in a special congressional primary runoff election in the conservative state.

Turnout was relatively light given that it was not a presidential or congressional election year, and voters were primarily hard-core partisans.

In New Jersey, with 99 per cent of precincts reporting, Christie had 60 per cent of the vote to 38 per cent for Democrat Barbara Buono, a state senator. He is the first Republican in a quarter-century to receive more than 50 per cent of the vote in New Jersey, a state that voted overwhelmingly for President Barack Obama last year.

"As your governor, it has never mattered where someone is from, whether they voted for me or not, what the colour of their skin was, or their political party," Christie said in his victory speech. "For me, being governor has always about getting the job done, first."

His triumph showed his ability to draw support from Democrats, independents and minorities. Christie now may have fodder to argue that that his emphasis on pragmatism over ideology makes him the most electable Republican in what might well be a crowded 2016 presidential primary field.

But it's not clear if Republican primary voters, who tend to be more conservative and ideological than the general electorate, will warm to the brash governor of a northeastern state. Republicans were fuming when, in the final days of last year's presidential campaign, Christie lavished praise on Obama for his response to a devastating storm that struck New Jersey.

In Virginia, McAuliffe, a former top Democratic Party official and close friend of Bill and Hillary Clinton, defeated Cuccinelli, the state attorney general. With 99 per cent of precincts reporting, McAuliffe had 48 per cent of the vote to 45 per cent for Cuccinelli, with Libertarian Robert Sarvis receiving 7 per cent.

McAuliffe, who characterized Cuccinelli as outside the mainstream, repeatedly cast himself as a dealmaker willing to compromise with a Republican-controlled state legislature.

"Over the next four years most Democrats and Republicans want to make Virginia a model of pragmatic leadership," McAuliffe said in his victory speech. "This is only possible if Virginia is the model for bipartisan co-operation."

Cuccinelli's candidacy was hurt by his ties to the small-government tea party movement, which is widely blamed for instigating last month's federal government shutdown. A large number of federal employees live in northern Virginia, where McAuliffe received the large majorities that finally put him over the top.

Preliminary results of an exit poll conducted for The Associated Press and the television networks found that about a third of Virginia voters said they were personally impacted by the shutdown, and nearly half said Republicans deserved the blame for it.

Cuccinelli also had to deal with a scandal involving the incumbent Republican governor, Bob McDonnell, who was barred by law from seeking re-election; a strong campaign by the candidate for the Libertarian Party, which favours a minimal role for government; and the tremendous fundraising prowess of his Democratic rival who heavily outspent him on TV ads.

Cuccinelli had hoped to score points in the final weeks of the campaign by highlighting the bungled start to Obama's signature health care overhaul. He emphasized that he was the first state attorney general to file a lawsuit to overturn the health law. McAuliffe had pledged to use the law to make 400,000 more Virginians eligible for Medicaid, the federal health program for the poor, under the new law.

In New York City, De Blasio's overwhelming victory over Republican Joe Lhota, a onetime Giuliani deputy, is seen as reflecting unease with the inequality of wealth among city residents, even as New York prospered over the past two decades. With 99 per cent of the precincts reporting, De Blasio, who ran on a tax-the-rich platform that contrasted sharply with Bloomberg's record, had 73 per cent of the vote compared with 24 per cent for Lhota.

"The people of this city have chosen a progressive path, and tonight we set forth on it together as one city," De Blasio told supporters at his victory rally.

Among other races, former health care executive Mike Duggan was elected mayor of Detroit, now undergoing the largest municipal bankruptcy in U.S. history. In Boston, Martin Walsh, a Democratic state representative, was elected to succeed Mayor Thomas Menino, who wasn't seeking re-election after more than two decades in office.