DOWNTOWN BROOKLYN (PIX11) — An argument that started over a group smoking on a Brooklyn-bound subway train escalated into an assault and robbery, according to police.

The incident began around 8:30 p.m. July 4 aboard a southbound Q train approaching the DeKalb Avenue stop in Downtown Brooklyn, when a group of five people were smoking on the train, authorities said Wednesday in a public appeal for tips.

A woman, 29, and a man, 32, who were aboard the train began recording video of the group, officials said.

The smoking straphangers took exception to being recorded, according to authorities. They got into a verbal argument with the victims, then punched and kicked them before fleeing the train when it arrived at the DeKalb Avenue station, police said.

After the assault, the male victim realized that the Apple Watch he had been wearing on his wrist was gone, officials said. First responders brought the victims to an area hospital in what authorities described as stable condition.

Investigators released surveillance footage of the suspects leaving the DeKalb Avenue station.

Submit tips to police by calling Crime Stoppers at 1-800-577-TIPS (8477), visiting crimestoppers.nypdonline.org, downloading the NYPD Crime Stoppers mobile app, or texting 274637 (CRIMES) then entering TIP577. Spanish-speaking callers are asked to dial 1-888-57-PISTA (74782).