Office workers scrambled for cover as a probation officer fired off a round while struggling with a man in Downtown Brooklyn yesterday, witnesses said.

No one was reported hurt in the 11:30 a.m. fight outside 14 Boerum Place, near Borough Hall.

The unidentified probation officer, who was on duty, struggled with Lee Rush, 40, in the officer’s personal car, police said.

During the fight, the officer’s gun went off once, frightening people nearby.

“I saw two men struggling on the floor outside these doors. I did not know one of them was an undercover cop,” said Carlos Irizarry, chief of security at 14 Boerum Place.

Police soon arrived.

“When the officers came, I said, ‘One of the guys has a gun! One of the guys has a gun!’ ” Irizarry said. “That’s when the guy popped up and said, ‘I’m an undercover!’ ”

Rush, who had a knife, was charged with weapons possession.