Shortly about 12:30 GMT on Wednesday, a Mercedes truck, a Nissan Juke, and a Volkswagen Polo were involved in an accident.
The man in his 30s who was driving the lorry died at the scene, according to Hampshire police.
A section of the motorway facing westward is closed until a new gantry is installed. The original one was damaged when the lorry caught fire.
Inspections by National Highways revealed that the nine-meter (30-foot) high structure that crosses multiple lanes would need to be replaced.
“This is a complex situation and removing the damaged gantry will take a number of hours,” stated Mark Hallett, operations manager. This nine-meter-tall bridge crosses several lanes of traffic.Our top priority is the safety of individuals using our network, and the safest method for us to remove the gantry is to keep the entire carriageway closed.
Work to remove the gantry began at midday. It is not clear how long the motorway will remain closed for.
The closure in is place between Fareham at junction nine and junction five. Traffic is being diverted at junction nine to the A27.
Two men, aged 32 and 37 and a woman, 40, have been arrested on suspicion of causing death by dangerous driving.
Police said the trio, all of of no fixed abode, remain in hospital, while a woman in the Nissan suffered minor injuries.
Officers asked anyone who witnessed the crash or those with dashcam footage to get in touch.
