Drivers on the A3 Portsmouth-London road are facing delays today after the northbound section of the Hindhead Tunnel was closed.
The carriageway was shut on Sunday as emergency repairs were carried out.
Northbound traffic was diverted along one lane of the southbound route through the tunnel.
A spokesman for the Highways Agency said delays of 30 minutes were expected, and advised drivers heading towards London to take a diversion onto the A31.
The closure is expected to be in place until 10pm today.