A 16-year-old cyclist was hit by two cars in quick succession in an apparent double hit-and-run, police have said.
The first crash happened on High Road, Streatham, south London, at 23:17 BST last night, Scotland Yard said.
It is thought a second car travelling close behind hit the boy seconds later. Both failed to stop at the scene.
The victim remains in hospital with life-threatening injuries. Police said two men were arrested at separate locations in the local area.
It is not thought the pair, both in their 20s, were known to each other.
They remain in custody as inquiries continue, police said.