PART of the Dartford Crossing will be closed overnight on Saturday.
Both tunnels of the northbound crossing will be closed for an emergency exercise with emergency services and tunnel staff.
The Southbound Queen Elizabeth II bridge will remain open to southbound traffic.
Emergency exercises are carried out on a regular basis to ensure that the Highways Agency and the emergency services are equipped and ready to deal with incidents that may occur within the tunnels.
The closure, between junction 2 (A2) and junction 31 (A1306), will be in place between 10pm Saturday and 4am Sunday.
A clearly signed diversion route will be in place on when both tunnels are closed via the A2, A201 Blackwall Tunnel and A13.
Drivers are advised to plan ahead and leave extra time for their journeys.
The Blackwall tunnel has a height restriction of 4.0m (13’0”) and is classed as ‘ADR Category E’ for hazardous goods. Any vehicles above this height restriction or carrying dangerous goods will be diverted via the clockwise M25.