Around 35 firefighters and officers attended the scene on Southend Arterial Road in Hornchurch, early this morning.
Six fire engines battled the blaze at a row of log cabins and a disused garage this morning, after being called just before midnight.
An attending officer said the buildings “went up in a giant fireball” and there was one fatality - a dog.
Emergency services shut the westbound carriageway towards Hall Lane whilst they tackled the blaze, which engulfed part of the office and shop in the garage.
A fire crew from Essex fire brigade was called to work alongside crews from Hornchurch, Harold Hill, Romford and Dagenham.
The cause of the fire is under investigation.
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