Residents have been warned to close windows and doors as firefighters have been tackling a "substantial" fire for over an hour.
Herts Fire and Rescue and Herts Police were called to Chorleywood Road, Rickmansworth, at around 4.11pm as smoke billowed from a two-storey home and can apparently be seen from the M25.
The carriageway has been shut by police officers between Loudwater Lane and the M25 while six engines work to try and put it out.
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It is understood that no one was trapped inside the building and everyone has been accounted for. People have been warned to avoid the area.
A witness who drove past the scene said the two-storey home was “well alight” already by around 4.15pm and is still not out as of 5.30pm.
Footage shows the newbuild property almost completely hidden from view beneath the rising cloud of smoke as a hose jet is used to tackle the blaze.
Herts Fire and Rescue are advising residents to keep their doors and windows closed.
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