Police have launched a murder investigation after a teenager was stabbed to death in the street.

The 18-year-old was targeted by a lone knifeman as he was walking in Old Trafford, Greater Manchester, on Wednesday afternoon.

Officers from Greater Manchester Police discovered the victim, who has not yet been formally identified, with stab wounds. He was taken to hospital where he died from his injuries.

A police spokesman said the motive for the attack in Upper Chorlton Road at around 2.20pm is not yet clear.

Chief Superintendent Jim Liggett, divisional commander for Trafford, said: "Our thoughts and deepest sympathies are with the relatives and friends of this young man. I cannot begin to imagine what they are going through and specially trained officers are offering them whatever support we can.

"We are still very much in the early stages of this investigation and all we know for certain is that this young man has been attacked in broad daylight as he walked along the street. At this time we are looking for one offender but the area would have been extremely busy so I would ask anyone who witnessed this to come forward. Undoubtedly, the answers to these questions may lie within the community and I would urge residents to stand side by side with us and help us bring this man's killer to justice."

He added: "If you know anything about the reasons why the victim was attacked, the circumstances leading up to it or the person responsible, you have an absolute responsibility to him, his family and to the justice process to do the right thing and let us know.

"We have a dedicated syndicate of experienced detectives investigating this matter and will do everything we can to bring whoever is responsible to justice. There is an increased police presence in the area as we continue our investigation and to reassure local residents so if you have any concerns or information you wish to provide please come and speak to us."

A post-mortem examination is due to take place later. Anyone with information is asked to call police on 0161 856 4711, or Crimestoppers anonymously on 0800 555 111.

The victim was given first aid by the side of the road when he was spotted by a Greater Manchester Fire and Rescue Service crew from Moss Side which was on its way back from a job. The crew pulled over and tried to save the teenager by giving him first aid and oxygen but the victim's injuries proved too severe and he later died.