These taggers work fast.

A Q train was completely covered in graffiti overnight at a Second Avenue subway station while it was parked just off the platform, according to photos and a transit activist.

Photos posted to the Progressive Action Facebook page show the colorful train parked at the 96th Street station at about 5 a.m., just before the start of the morning rush hour.

Train conductor Tramell Thompson, a transit activist who runs the Progressive Action page, said it appears that the tagger got to the train while it was parked just off the platform overnight — and that should be a warning to city transit officials.

“If they can go back there and have the time to do all of that graffiti, they have time to do something to the train,” Thompson said. “It’s obvious they have no security back there.”

MTA officials declined to comment on the incident or say how long it took to take the train out of service.

NYPD officials didn’t return requests for comment.