Fire crews are still tackling a large blaze at a recycling centre in Potters Crouch.
Four engines, including two from Welwyn and one from Watford, have been at the site overnight and remain there this morning. The blaze has been burning in Appspond Lane since 1am on Sunday morning.
Staff from the National Grid are also at the scene making sure that the overhead power lines in the area are safe.
The A414 and the A4147 remain closed and it is not known when they will reopen.
Hertfordshire County Council has said that steady progress is being made.