An 18-year-old man is in a critical condition in hospital after reports that his off-road bike struck a stationary car, police said.
Officers then arrested two men on suspicion of obstructing them from helping the man, who had crashed on St Helens Road, Bolton, at about 22:18 BST on Saturday.
A force spokesperson the man was given first aid before he was taken to hospital with serious injuries, where he remains in a critical condition.
The two men were arrested on suspicion of obstructing police and a Section 5 Public Order Act offence.