A 30-year-old woman had her $35,000 engagement ring stolen right off her finger by a sly thief in Manhattan, police sources said.

The victim was on W. 18th St. near Fifth Ave. when the thief bumped into her and slipped the platinum ring, containing 16 full cut diamonds, off her hand around 12:30 p.m. Thursday.

The victim told cops that the crime happened so fast she could not tell who bumped into her.

No arrests have been made and police are still looking for the suspect.

The victim is the sister of a former aide to Sen. Chuck Schumer, sources said.