The Louis-Hippolyte-La Fontaine Tunnel is completely closed (southbound direction) until the end of Sunday.
Road work is underway at the southbound exit.
Police officers are stationed at the exit all day for traffic control.
Transport Quebec is asking drivers to avoid the area, if possible, and use either the Champlain, Jacques-Cartier or Victoria Bridges to cross the river.
The city of Montreal is temporarily removing parking spots on Papineau Street, between Crémazie Boulevard and the Jacques-Cartier Bridge, to encourage traffic flow. This measure is in place until 7 p.m. Sunday evening.
Public transit authorities are increasing metro service on the yellow line serving Longueuil during the tunnel closure.
Drivers travelling between Quebec City and Montreal are urged to take Highway 40 instead of Highway 20.