Two lanes have opened in both directions between junction 25 and 27 although a 40mph speed limit will be in place through the scene for safety reasons.
The road has now re-opened at junction 23 to 25.
Following the incident which happened at 2am this morning, where a HGV crossed over the central barrier into the opposite carriageway and collided with other vehicles, there will be a need to resurface the road this evening due to the damage to the carriageway.
There are severe delays in the area and drivers are strongly encouraged to allow extra time for their journey.
There has also been another incident on the M25 anti-clockwise between junction 28 and 27. However, this has been cleared to the hard shoulder.
The Highways Agency provides live traffic information via its website, local and national radio travel bulletins, electronic road signs and mobile platforms, such as the iPhone.
Members of the public should contact the Highways Agency Information Line on 0300 123 5000.
Journalists should contact the Highways Agency press office on 0844 693 1448 and use the menu to speak to the most appropriate press officer.