Polls will remain open until 8 p.m.
"It's dead and double dead," Nick Sodano, Democratic chairman in Mount Holly, said of turnout after casting his own ballot.
He said he voted because there was a contested municipal election, and that gridlock in Congress would not inspire turnout.
James Bilyard, a Mount Holly resident for 65 years and regular voter, also cited the local race.
"A former councilman is running today and I wanted to give him a chance," he said.
Robert E. Andrews, a Democrat who had represented the First Congressional District for 13 terms, left office earlier this year to take a job with a Philadelphia law firm, while Jon Runyan, a Republican, is giving up his seat in the Third Congressional District when his term ends in January.
State Sen. Donald Norcross (D., Camden), brother of South Jersey Democratic power broker and businessman George E. Norcross III, announced his candidacy to replace Andrews almost as soon as the congressman announced his resignation in early February. With name recognition and organizational backing, Norcross is considered the front runner.
Two other Democrats filed ballot petitions for a chance at the seat: Frank W. Minor, 59, in his third term as mayor of Logan Township; and Frank C. Broomell Jr., 27, a graduate student and Marine Corps veteran, from Sicklerville. The district, covering parts of Camden, Burlington, and Gloucester Counties, is staunchly Democratic.
The Republican field includes food-equipment repairman Lee Lucas, 56, of Gibbstown; former Philadelphia Eagle and now sports-radio talk-show host Garry W. Cobb, 57; real estate professional Gerard McManus, 47, of Berlin; and small-business owner Claire H. Gustafson, 62, of Collingswood. Cobb, with his famous name, NFL resume, and party endorsements, is considered the favorite.
In the Second Congressional District, Republican incumbent Frank LoBiondo, 68, who was first elected to the office in 1994, has a much bigger war chest and is favored to beat challenger Mike Assad, 27, a former Absecon school board member, in a repeat of the 2012 Republican primary.
Among the Democrats, Bill Hughes Jr., 47, of Northfield, a lawyer with Atlantic City's Cooper Levenson firm, has earned most of the endorsements from the Democratic establishment and has raised significantly more money than his primary challenger, Dave Cole, 28, of Sewell, a former Obama administration staff member and tech-industry executive.
The sprawling Second District includes the counties of Salem, Cumberland, Cape May, and Atlantic and portions of Gloucester, Camden, Burlington, and Ocean.
Two former mayor from North Jersey, Tom MacArthur and Steve Lonegan, are duking it out in the heated Republican primary to replace Runyan in the Third District, which covers parts of Burlington and Ocean Counties.
MacArthur, 53, a millionaire former insurance executive, was mayor of Randolph in Morris County last year. Lonegan, 58, a conservative activist and former longtime Bogota mayor, moved from Bergen County.
Both moved to South Jersey to run.
MacArthur has sunk $2 million of his own money into the race - accounting for nearly all of his donations. He has been endorsed by Runyan and most of the district's elected officials and party establishment. Lonegan has run unsuccessfully for state and federal office five times, including the special U.S. Senate election won by Booker last year.
The winner of Tuesday's GOP primary is expected to face a competitive general election in November. Burlington County Freeholder Aimee Belgard, 40, of Edgewater Park, is the favorite to win the Democratic nomination over lawyer Howard Kleinhendler, 50, of Brick, and Bruce Todd, 64, of Waretown, who ran last year as an independent Democrat for lieutenant governor.
Democrats last won the seat in 2008 with the late U.S. Rep. John Adler, who held it for just one term before Runyan won it back.
Booker is running unopposed in the Democratic primary for U.S. Senate. Four candidates - Jeff Bell, Murray Sabrin, Brian Goldberg, and Richard Pezzullo, none of whom has ever held public office - are running for the Republican nomination to face Booker in November.