The aide spoke on condition of anonymity because he was not authorized to publicly discuss the death before it was formally announced.
Lautenberg was the U.S. Senate's oldest member.
He reportedly had been sick for some time. His last appearance on the Hill was in a wheelchair. A bout with the flu caused him to miss the Senate's Jan. 1, 2013 vote to avoid the fiscal cliff of rising taxes and falling government spending.
Lautenberg was diagnosed in February 2010 with lymphoma of the stomach and underwent chemotherapy for the next few months.
He was a multimillionaire businessman and liberal who was called out of retirement for a second tour of duty in Congress. He was principal sponsor of a law banning smoking on domestic airline flights.
A statement is reportedly forthcoming from his office.
Lautenberg was 89 years old.
(The Associated Press contributed to this report.)
