A teenager subjected to a terrifying sex assault was saved when her screams for help were heard by a passer-by.

The 18-year-old victim, who had been visiting a friend, was walking home in the early hours of Saturday morning when she was attacked from behind.

A man in his early 20s, who spoke with poor English, asked her for sex and when she refused he grabbed her hair and dragged her to the floor.

The girl was pinned to the floor as the Asian-looking attacker covered her mouth and tried to rape her at around 2am in Leybourne Terrace, Stockton.

Detective Constable Jeremy Collins said it was a "nasty" assault and, although the victim received no physical injuries, she was left badly shaken.

He told how the girl was saved when her screams were heard by a man nearby who intervened and chased the assailant.

DC Collins added: "It was fortunate he heard her screaming for help and his intervention stopped the attack."

The Good Samaritan pursued the attacker along Leybourne Terrace but lost sight of him when he ran down a dark alley.

The attacker, who had black gelled hair, wore a light brown or dark grey-coloured leather jacket and light blue jeans. Police are appealing for witnesses to contact 01642 302226.