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Highways England
The M25 in Hertfordshire is closed anti-clockwise after a lorry crashed into the central reservation and shed its load of sanitary products.
The crash happened just before 16:30 BST at J18 near Chorleywood, causing the unspecified products to spill on to the opposite carriageway.
Both carriageways were closed to allow an air ambulance to land, but two lanes clockwise have since reopened.
Hertfordshire Police said "significant" traffic disruption was expected.
There is a queue of about seven miles anti-clockwise with conditions not expected to return to normal until 23:00, according to Highways England.
A police spokeswoman said the products were "non-hazardous" but was unable to provide any more information.