A woman who witnessed a "brutal" group attack on a teenage boy said she is "deeply concerned" for the victim.

Sarah Jane Palmer was shopping in Sainsbury's supermarket in Fortis Green Road shortly before 9pm on November 9 when she heard screaming outside.

Rushing outside, she saw a large group attacking a boy in the road and yelled at them to stop.

She wrote on Facebook: "They had a knife and were repeatedly punching and kicking him while he was on the ground pinned down by the entire group attacking him in the middle of the road," she said.

"I yelled at them to get off him and surprisingly they did, but the attack was sustained and began when I was still in the shop."

The victim fled, but Ms Palmer said she comforted his friend and spoke to police but nobody could locate the victim.

She said they tried to call his phone but believed it was found by someone else, who answered it.

She added: "I’m deeply concerned for the boy who was attacked.

"It was only about a month ago I witnessed teenage boys in Alexandra Park Road pull a knife and steal a scooter from other teenagers in broad daylight."

She believes police know many of the teenagers that were out on Muswell Hill Broadway on November 9.

She said: "The police were doing a good job to break up the crowds and arrest people. It’s an admirable and extremely difficult job.

"I’m deeply saddened but also I worry it is not safe even in Muswell Hill for young people.

"I wonder what our community can do to help stop all this violence."

A Metropolitan Police spokesperson said: "Youth violence has a devastating and lasting impact on victims, and the wider community and we understand that witnessing a crime in progress can be extremely distressing."

Anyone that has information about violent crime, or has concerns about crime in their community, should contact the police on 101 or speak to Crimestoppers anonymously by calling 0800 555 111.

In an emergency always dial 999.