A woman, 80, remained in a life-threatening condition after a BMW i3 crashed into five other vehicles on Warrington Road in Ashton-in-Makerfield at about 13:00 BST, leaving four people in hospital.
Greater Manchester Police said the BMW driver suffered a suspected medical episode before the crash. Two drivers and two passengers were taken to hospital after emergency services arrived at the scene.
The woman, 80, was among those hurt in the collision. A man in his 70s and another woman were being treated for serious but not life-threatening injuries, while a man in his 80s had minor injuries.
The crash turned a busy stretch of Warrington Road into an emergency scene in broad daylight, with police and paramedics dealing with multiple vehicles and several casualties at once. Officers from GMP's serious collision investigation unit are now leading the inquiry.
That investigation will focus on how the BMW came into contact with five other vehicles and whether the suspected medical episode was the trigger. Police are urging anyone who saw the collision, or who has dashcam footage, to contact them.
The immediate question is whether the woman in hospital can be stabilised and whether witness footage can fill in the seconds before impact. For investigators, the case now hinges on what drivers saw on Warrington Road before the BMW struck the other vehicles.
