Firefighters battled a blaze at a disused factory building in St Neots.
At 4.29am today (Monday), crews were called to Cromwell Road, where they found a rapidly developing fire and quickly called for back-up.
The fire was affecting half the ground floor of the two-storey building, which measures approximately 20m by 30m. The entire building was filled with smoke.
Firefighters wearing breathing apparatus used five jets, two hose reels, and two hydrants to put the fire out by 7.12am.
One crew from St Neots, one crew from Gamlingay, one crew from Huntingdon, one crew from Kimbolton, one crew from Papworth, one crew from Bedford, one crew from Cambridge and a support crew from Huntingdon attended.
The incident was then scaled down and three crews remained at the scene dampening down and checking for hotspots with a thermal imaging camera.
Police closed Cromwell Road while the incident was ongoing. A spokesman confirmed that the road remained closed at the last update which was given at just after 9am.
At 9am, one fire crew from St Neots also remained at the incident. The building is believed to be structurally unsound now as a result of fire damage.
Incident commander Paul Clarke said: “The first crews did well to recognise the scale of the fire and having the extra crews there so quickly meant that we could surround the fire and bring it under control quickly.
“A full fire investigation will take place this morning but early indications are that it was started deliberately.”