WALTHAM (CBS) – Waltham Police are warning residents of “unprovoked, random assaults” that have taken place in the city in recent weeks.

Police say at least 10 people in the city of Waltham have been assaulted at different locations since Nov. 10. The most recent one occurred on Friday night, according to Waltham Police Detective Sgt. Steve McCarthy.

The victims have been alone, struck from behind or without provocation. The attacks have occurred between 5:30 p.m. and 11:30 p.m.

At first, the attacks were going on at the GardenCrest Apartment Complex in Waltham, but police now say there have been recent incidents in the downtown areas of Chestnut Street and Charles Street.

A Waltham resident who was attacked at the GardenCrest Apartment Complex told WBZ-TV in Spanish that he is afraid to return to the area he was assaulted.

“I came to smoke here in the back and suddenly somebody came from my back and hit me with something. Something heavy,” the resident said through a translator.

The victim say he has a fractured skull and some internal bleeding. He also said that while he’s healing slowly, he is still afraid because the attacker has yet to be arrested.

It is not clear how many people are involved, and descriptions of the assailant have varied. Police are asking residents to be aware of their surroundings, especially at night.

“It’s really scary to come out at night now, because you never know,” said Waltham resident Donna Roland. ““I stay home. As soon as it gets dark, I stay home. I don’t want to come out now.”

Anyone with information is asked to call Waltham Police at 781-314-3600 or at their anonymous tip line, 781-314-3636.