A boy who saw a police car plough into a young woman as it responded to a 999 call said the officer beeped the vehicle's horn moments before the fatal crash.

The teenager was walking along the main road in Walthamstow, east London, when he witnessed the woman's body being "thrown into the air" and "sliding across the road".

The marked police car was speeding down Forest Road after receiving a 999 call late last night (TUES).

But the flashing car crashed into the 21-year-old Ethiopian woman who was staying at the YMCA hostel just yards from where she was killed.

The teenager, who lives across the road from the scene of the horror crash,said: "Me and my mate hang out at the YMCA and we were leaving, it was around 11.45pm.

"We heard the sirens and saw the blue flashing lights. Then we heard him beep the car's horn.

"Two seconds later we see a body slide across the road. We thought it was a fox.

"If the curb wasn't there, then she would have have gone further.

"We ran over there and shouted. The policeman was panicking.

"I think she was crushed and the car was a write off.

"The windscreen was shattered. She was thrown up and slid across the road."

His mum said she woke up to hear him sobbing and banging on their front door, shouting "mummy, the policeman killed a girl."

She said she and her son were awake until the woman's body was finally taken away after 6am.

The 18-year-old added: "Another police car arrived, all you could hear was sirens.

"My mate was really upset, we are losing our trust in police as it is."

Another resident, who gave his name as Ozzie, 19, said: "I come to meet my friend in the college and work nearby.

"When I came by at 8am the road was still blocked off. I thought there was a stabbing.

"I asked an officer and he said just a crash, just casual. Then someone told me a police car crashed into a woman. It is funny how a police officer said something different.

"I am surprised because police officers need to obey by rules too."

A YMCA spokesman confirmed the young woman lived at the residence on Forest Road.

He said: "A resident at YMCA Walthamstow was involved in a fatal car incident last night on Forest Road.

"The road has been shut as an investigation takes place.

"YMCA St Paul's Group is shocked and saddened by this news and wishes to extend its condolences to the family and friends of the resident."

A Met Police spokesman said: “The police car had been responding to an emergency call to a man threatening members of the public at a location in Walthamstow.

Both the Directorate of Professional Standards and the Independent Office for Police Conduct (IOPC) have been informed."