Newark Mayor Cory Booker (D) is collecting signatures to run in the special election to replace Sen. Frank Lautenberg (D-N.J.).

Booker hasn't formally entered the race, but spokesman Kevin Griffis told The Hill the mayor's team is collecting signatures to join the ballot. Any candidates hoping to run in the race must file 1,000 signatures by 4 p.m. on Monday.

"Yes. Our volunteers are collecting signatures, which is consistent with what we've been doing for the last several months — taking the steps necessary to run. We will make an official announcement at the appropriate time," he said in an email.

The news was first reported by The New Jersey Star-Ledger.

Gov. Chris Christie (R-N.J.) set a special election for Oct. 16 after Lautenberg died on Monday. The primary is set for Aug. 13.

Booker is seen as a favorite in the race, and multiple sources have said he plans to run. Reps. Frank Pallone Jr. (D) and Rush Holt (D) are expected to challenge him.

Because of the blue tint of the state, whomever receives the Democratic nomination is likely to win in the general.