One of the collisions involved a HGV, which appears to have crashed into the side safety barrier before spinning out of control. The lorry is now blocking the carriageway.
Essex Police Southern Roads Policing Unit confirmed the driver was unhurt in the crash, but warned the motorway may remain closed for numerous hours.
Essex police issued a statement, saying: “We’re currently at the scene of a collision on the M25 between J30 and J29 anti-clockwise.
“The road will remain closed for several hours causing significant delays. Road closure likely to affect A13.
“Avoid using routes where possible. Allow extra time for your journey.”
Neil Pudney, district commander for Southend, added: “Just finishing a shift as night silver commander. M25 shut anti-clockwise from junction 30 to 29 due to a vehicle accident.
“Unlikely to open for at least 2-3 hours so please try to avoid area and make alternative travel plans.”
A full road closure is currently in place, and the vehicle is only expected to be cleared by around 8.45am, according to Highways England.