Two people have died after a "serious incident" on the M1 motorway.
Hertfordshire Police and the East of England Ambulance Service were called to the incident on the northbound carriageway near Junction 5 at about 10.45am.
It is understood two people died but officers are working to establish the circumstances surrounding the deaths.
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Footage taken from a motorway CCTV camera appeared on Twitter, which seemed to show emergency services working on a bridge above the scene of the incident as well as on the road below.
A police spokesman said: "Police are currently attending a serious incident and are asking drivers to avoid the area where possible.
"The southbound carriageway had been closed but is now open. However, the northbound carriageway is closed and is expected to remain closed for some time.
"Drivers are thanked for their patience but asked to find alternative routes where possible."
A spokesman for the ambulance service said two ambulances, an emergency response vehicle and an air ambulance had been dispatched to the scene but were stood down after midday.