The 16-year-old was left fighting for life with terrible burns from the drain-clearing chemical.

She was under heavy sedation at a specialist burns unit last night as sickened police called the attack by five youths a new low.

The gang beat the teenager before taking turns to rape her in an empty house in Tottenham, North London.

One detective said: “After they had finished raping her, the gang poured caustic soda over the girl to try and get rid of DNA evidence. It was the most horrific thing imaginable and the girl sustained serious burns. This is about as low as it gets.”

A woman cop living next door was alerted by the victim’s cries — and the officer treated her until medical help arrived.

Another neighbour said: “I heard a woman screaming, ‘Help, I’ve been raped’ and saying she had been burned. She sounded in a lot of pain.”

One resident, who did not want to be named, said: “The gang get up to no good.

“They told me they took the girl and broke into the house and that one of them threw water over her — but I have heard it was acid.”

Doctors feared the girl would die but she pulled through and is now stable in a burns unit in Billericay, Essex. She is still not well enough to speak to officers.

A police source said: “She has appalling injuries from which she will never fully recover. We believe it will be another two weeks before we can interview her.”

A 17-year-old was arrested over last Wednesday’s attack.

But he was taken to hospital claiming to have swallowed a 10p coin.

Cops are waiting to talk to him.

Anyone with information on the attack, said to have been by five black youths, should call Crimestoppers on 0800 555111.