Republican Chris Christie has been re-elected governor of New Jersey, US media project.
Gov Christies beat easily his Democratic challenger, state Senator Barbara Buono, CNN, CBS and NBC said. Official results are expected shortly.
In the Virginia governor election, the race is too close to call, the US media say.
New York City is choosing a successor to three-term Mayor Michael Bloomberg, a Republican-turned-independent.
Tuesday’s races are the first major round of elections since President Barack Obama won a second term in the White House one year ago.
They are seen as an early test of the Republican and Democratic parties’ strengths ahead of next year’s critical congressional mid-term elections.
New Jersey victory
In New Jersey, Mr Christie, 51, was declared the unofficial winner by the US media just minutes after the polls closed.
Meanwhile, Ms Buono has struggled to gain traction.
Analysts say Mr Christie’s popularity with voters in Democratic-leaning New Jersey makes him a contender for the 2016 Republican presidential nomination, because it could enable him to claim broad political appeal.
Mr Christie was already a popular figure when Superstorm Sandy devastated the state’s coastline a year ago. His response to the storm attracted national attention.
He has been campaigning across the state since last week, even as polls suggested he had an advantage of at least 20 points on Ms Buono.
While many in New Jersey support her positions, she has had difficulty raising money, even from Democrats, because of her relatively low profile.
New York race
In New York City, Democratic mayoral candidate Bill de Blasio has taken a commanding lead in opinion polls over Republican Joe Lhota, a former senior official in the mayoral administrations of Mr Bloomberg and his predecessor Rudolph Giuliani.
Mr de Blasio, the city’s public advocate, ran Hillary Clinton’s 2000 Senate campaign. He is seen as one of the most liberal mayoral candidates in decades.
Under Mr Bloomberg, Mr Lhota ran the city’s public transport authority. He was lauded for quickly getting the vast subway system running again after a huge storm, Sandy, flooded swathes of the city last year.
The polls in the Virginia governor race have now closed, with Democrat Terry McAuliffe pitted against Republican Ken Cuccinelli.
Mr McAuliffe is a businessman and veteran Democratic party fundraiser. He has close ties to former President Bill Clinton and Mrs Clinton, serving as chairman of her 2008 presidential campaign.
Mr Cuccinelli, the Virginia attorney general, has angled for the support of the hardcore conservative Tea Party movement of Republicans.
Mr McAuliffe, who has raised much more money, has sought to link Mr Cuccinelli to last month’s partial shutdown of the federal government, which was brought about by Republicans in Washington DC.
Virginia, long a Republican stronghold, has seen a demographic shift in recent years. Mr Obama, a Democrat, won the state in the last two presidential elections.
The results of Tuesday’s polls could prove an early measure of the parties’ support ahead of the midterm elections of 2014, which will decide the make-up of the House of Representatives, one-third of the Senate, and the governorships in more than half the states.
In Washington, Mr Obama’s Democratic party controls the Senate, while the Republicans hold sway in the House of Representatives. Now in his second term, Mr Obama will vacate the presidency in 2017.