The A1(M) southbound is closed between Junction 3 (St Albans/Hatfield) and Junction 1 (M25) following a serious collision.
Hertfordshire Police are leading the response and have said the closure is required to allow for detailed collision investigation work, vehicle recovery and safety checks.
“These processes are complex and time-consuming and require the carriageway to remain fully closed to ensure the safety of those working at the scene,” National Highways said.
Details of the incident are still being established.
The closure is expected to remain in place throughout the night.
This is an ongoing event and updates will be provided.
