Part of Chorley New Road was closed for around seven hours as emergency services dealt with the incident.
Police and ambulance crews were called to the scene between Regent Road and Beaumont Road at 5.15 this morning.
It's been confirmed that a car has crashed into a tree and four people were involved with one of them being described as being in a serious condition.
Two of the passengers in the car had to be cut out by fire crews.
An investigation is now underway.