A three-year-old boy was seriously injured when he was hit by a van being pursued by the police.
Police officers on patrol attempted to stop a stolen vehicle on Wigan Road, Westleigh, shortly after 10.35am on Tuesday.
The white Ford Transit Connect van failed to stop and there was a brief pursuit, during which the van hit the three-year-old near the Tamar pub, at the roundabout with Nel Pan Lane.
Police said the van did not stop and drove off towards Twist Lane.
The police officers immediately stopped and gave first aid to the boy until paramedics arrived. The air ambulance also attended but was not used.
The boy was taken to hospital for treatment, where he remains in a serious condition.
The van has since been found nearby and police are working to trace those responsible, with support from the force helicopter and police dogs.
Wigan Road remains closed between Nel Pan Lane and Hill Crest Avenue as the investigation continues.
Greater Manchester Police said the incident had been referred to the professional standards branch in line with normal force policy.
Insp Danny Byrne, from the force's serious collision investigation unit, said: “This was a horrendous incident that has left a four-year-old boy in hospital fighting for his life and we are doing all we can to support his family at this incredibly difficult time.
“Our investigation is continuing very quickly as we have deployed several resources – including the helicopter and police dogs - to support our efforts to trace those responsible.
“I am urging anyone that thinks they might have seen the van throughout the morning or have any information, no matter how small or insignificant it might seem, to please get in touch as soon as possible.
“Even the smallest piece of information could be the key to us finding those responsible so please call police.”
Anyone with information is asked to call the serious collision investigation unit on 0161 856 4741 or 101, quoting reference 628 of October 30.
Reports can also be made anonymously through the independent charity Crimestoppers on 0800 555 111.