Police investigating the stabbing of a 16-year-old boy at his friend's house are appealing for anyone who saw a young man in an agitated state to come forward.

The victim, named locally as Luke Kennedy, is in a critical but stable condition in hospital after he was airlifted from Fitchet Close, Crawley, on Monday evening.

A 14-year-old boy arrested in connection with the stabbing was being questioned by detectives at Crawley police station as the victim fought for life.

Police have also been searching for a knife in relation to the incident.

Det Chief Insp Trevor Bowles, of Sussex Police's major crime branch, said: "We are urgently searching for a knife which we believe was discarded nearby. We are keen to talk with anyone who has information about its whereabouts."

Mr Bowles also appealed to anyone who saw a young man emerge from a house in Fitchet Close in an agitated state to come forward with information.

Luke had been visiting a friend at the house when he was stabbed. The friend's mother administered first aid before the ambulance crew arrived, a Sussex Police spokesman said.

He was then airlifted to the Royal London Hospital in Whitechapel, east London, for treatment to a single stab wound to his upper back.

Police originally reported that the teenager had been stabbed repeatedly but it later emerged that other "wounds" on his body were as a result of medical aid.

Armed officers later contained a property in Ifield Drive, Ifield, before going to Chiltern Close, West Green, where at 7pm on Monday they arrested the 14-year-old boy.

Two uniformed police officers have been standing guard outside the property in Fitchet Close where Luke was found.

Anyone with information is asked to contact Sussex Police on 0845 6070 999, quoting Operation Kinsale, or Crimestoppers, anonymously, on 0800 555111.