A man was beaten with a chain in an unprovoked attack aboard a BART train during Tuesday evening commuting hours, leaving him with injuries that required hospital treatment, officials said.

The unidentified victim was on a Daly City-bound train approaching Lake Merritt Station shortly after 6 p.m. when another man allegedly asked for directions and then hit him, according to BART spokesman Jim Allison.

The attack was unprovoked, a witness told police. The suspect hit the victim and struck him with a chain that BART officials said was possibly a bike lock.

The suspect fled the train at Lake Merritt Station and has not been apprehended. He is described as a white man in his 30s wearing a white t-shirt, black sweatpants and a beanie and carrying two plastic bags.

The victim was taken to a local hospital with non-life-threatening injuries for treatment.

Anna Bauman is a San Francisco Chronicle staff writer. Email: anna.bauman@sfchronicle.com Twitter: @abauman2