A man in a baseball cap emerged on a West Village street through a sidewalk grate and threw a smoke bomb into a crowd of restaurant diners before fleeing back into the grate Friday evening, police say.

The man popped up from underground outside Bar Pitti on Sixth Avenue between Bleecker and Houston, lobbed a smoke bomb into the outdoor patio area, then went back through the grate, which leads to the subway system, according to police.

The smoke bomb resembled a red safety flare as it went off, according to a witness.

No one was hurt, authorities say, but diners were shaken.

"We were just trying to relax and have a nice dinner, and then there was smoke and a bunch of policemen," said Sara Bond, who was visiting from New Orleans.

Australian tourist Tina Millet said it was "quite a big commotion."

"I've seen everything in New York, absolutely everything," she said.

It also sparked questions of how secure the city's subway system is. Neighbor Monica Vickers said she immediately wondered whether the smoke bomb was terror-related.

"I guess they're going to have to do more security or something, right?" she said.

Police haven't said how they think the man was able to get underground and up through the grate.

The suspect was described as a man in his 30s with blonde hair, wearing a baseball cap and a T-shirt with an American flag on it.

Follow Brynn Gingras on Twitter @Brynn4NY