An 18-year-old man was killed and another seriously injured when the scrambler motorbike they were riding crashed with a car in south Liverpool.
It happened on Booker Avenue near to West Allerton railway station at about 20:40 GMT on Monday, police said.
Police believe the bike was stolen and was travelling in tandem with another when it crashed with a VW Tiguan, carrying two children aged nine and 11.
Witnesses reported neither of the bikes had any lights on.
The second bike initially stopped and then made off towards Mather Avenue.
The injured man remains in hospital in a serious condition, Merseyside Police said.
Ch Insp Kevin Chatterton said: "We are keen to speak to anyone who witnessed the collision, or saw the two scrambler bikes prior to the collision."