A man in a creepy doll mask has been terrorising Philadelphia residents, running up to them and making threats, police said.

The Philadelphia Police Department said on Tuesday it is searching for the suspect, who allegedly threatened and chased at least half a dozen people near City Hall last week.

The man, who surveillance video captured wearing a scary doll mask, asked a woman if she was “ready to die”, police told the BBC’s US media partner CBS.

Police released photos and a video of the suspect, seeking the public’s help to identify him.

In an incident on 12 August, the man was captured on surveillance video chasing a woman on a morning run around 5:30 local time (10:30 BST).

The masked man made threatening comments while holding his hand behind his back, causing her to stumble and injure herself, police said.

He then fled into a underground rail station.

The man appears to be filming the incidents, holding a cellphone with its light on, Philadelphia Police Department Captain Jason Smith told CBS.

It is unclear if the encounters are part of a social media trend, he said.

The suspect is facing charges including terroristic threats, simple assault and other offenses, according to the police captain.

Luanda Marinho told CBS she encountered the masked man while meeting a friend for a morning run.

“He starts asking, ‘Do you guys want to race me? I bet I am faster than you. Want to race me?’ He asked a few times, but none of us acknowledged him. Very weird,” Marinho recounted.

They are considering changing their running route, she said. “It was just weird, like some twisted game.”