Early reports indicate that a massive explosion has shaken the Hemel Hempstead industrial estate.
The fire at a recycling plant in Maxted Close, is believed to have started in a skip.
Surrounding businesses have been evacuated, the black smoke plume is not believed to be dangerous but is being investigated by fire officers.
Emergency services have put a 200 metre cordon around the building in case there are more explosions
A spokeswomen for Hertfordshire Police said roads around the premise were being closed by officers and buildings nearby were being evacuated.
Currently local roads have been closed.
We will keep you updated on any further developments.
A4147 Hertfordshire - Leverstock Green Way closed both ways between the A414 Breakspear Way junction and the Eastman Way junction in Hemel Hempstead, because of a building fire at an industrial estate.