F.B.I. personnel killed a man on Wednesday morning who was suspected of holding people hostage in an office building in downtown Bakersfield, Calif., ending an overnight standoff, the police said.

The shooting happened at around 4:20 a.m. on Wednesday, the Bakersfield police said, more than 15 hours after reports of a standoff that involved reports of a bomb threat in a building that houses a Chase Bank branch.

The suspect was pronounced dead at the scene, the police said. The authorities did not say how many people had been held hostage, but they said that all of the hostages were unharmed and had received medical treatment.

The Police Department said earlier on Tuesday that it first received a call reporting a bomb threat around 1 p.m. on Tuesday. A man had barricaded himself on one of the building’s upper floors with several hostages, the police said.

Two people were released after negotiators communicated with the suspect by phone, the police said on Tuesday.

The F.B.I. “assumed SWAT operations” in the standoff late on Tuesday, according to Sally Selby, a spokeswoman for the Bakersfield police, who did not give further details. The situation remained active into Wednesday morning, according to an email from the F.B.I.’s Sacramento field office that was sent around 2:30 am. The agency had said earlier on social media that it was supporting the response.

In a statement, Mayor Karen Goh of Bakersfield asked people to avoid the area to allow police officers and negotiators “to safely carry out their duties.”

The episode unfolded as votes were being cast in California’s primary elections. State Assemblywoman Jasmeet Bains, a Democratic candidate for Congress, canceled an election night watch party that had been scheduled for Tuesday in downtown Bakersfield.

Mark Walker contributed reporting.