A couple walking near Fisherman's Wharf Thursday morning were the victims of a surprise attack, when a man started beating them with a weapon seemingly without provocation.

Police say that the assault happened at 8:42 Thursday morning, near the heavily-trafficked intersection of Bay and Kearny Streets.

According to the San Francisco Police Department, a 45-year-old man and a 44-year-old woman were suddenly approached by the 39-year-old male suspect.

"Without reason," police say, the suspect "proceeded to strike them with a weapon causing injury."

That weapon, according to the SFPD, was a "metal pipe," which caused injuries to both victims that were significant enough to require transport to an area hospital for treatment. Both are expected to recover, police say.

Police say that the beating suspect was arrested and booked into San Francisco County Jail. The motive for the beating, if there is one, remains unknown as of publication time.