With almost 60 percent of the districts reporting, Lautenberg had 64 percent of the vote to 30 percent for U.S. Rep. Rob Andrews, New Jersey Network reported. A third candidate, Morristown Mayor Donald Cresitello, was in single digits.
On the Republican side, former Congressman Dick Zimmer had 46 percent of the vote to 39 percent for state Sen. Joseph Pennachio and 15 percent for Murray Sabrin, a libertarian college professor.
While turnout was low, the Democratic vote was about 50 percent higher than among Republicans. New Jersey has not had a Republican U.S. senator for more than 30 years.
Andrews made an issue of Lautenberg's age. The senator would be 90 by the time he completes a fifth term.
Republicans are struggling to keep the congressional seat being vacated by Rep. Mike Ferguson, who is stepping down after one term. State Sen. Leonard Lance won a seven-way primary, where the field included Kate Whitman, daughter of former Gov. Christie Whitman.
Democrat Linda Stender, who almost defeated Ferguson two years ago, had no opposition in the central New Jersey district.