The motorway is shut Junction 3, at the slip road to the M271, and Junction 4 at the turn-off for the M3, until 6am on Monday. It closed at 9pm on Friday.
Roadworks are taking place to finish the final stage of the £19m project to replace the old Romsey Road bridge.
Yesterday there was concern some of the diversion signs had been tampered with by unknown people, a council said.
Man dies after dog attack at Hillson Drive recreation ground in Fareham - owner is arrested
Fareham dog attack: Shrine set up in memory of man who died - named locally as Wiggy Symes
Heartfelt tributes paid to Wiggy Symes who died after Fareham dog attack
Fareham dog walker and trainer Ian 'Wiggy' Symes thought to be killed by XL American Bully breed dog
Thunderstorms yellow weather warning issued over Waterlooville, Fareham and parts of Hampshire by Met Office with chance of 'heavy rain'
Highways England has put a 55-mile diversion in place for westbound drivers, taking them up the M3 and westbound on the A303 to reach their destination.
The agency yesterday said: ‘Thank you for your patience. We're on schedule to reopen the motorway by 6am on Monday morning.’
The diversion is needed to avoid country roads around the roadworks site becoming gridlocked over the weekend, the agency said.
It is the third time in the last couple of years that the route has been closed for roadworks – and both times the road reopened earlier than the initial time given.
SEE MORE: When the M27 closure will start and end
For the final weekend closure, Highways England will be demolishing the old Romsey Road bridge and the motorway has to be shut to allow this to happen safely.
A new bridge was opened to vehicles and pedestrians in December 2019.