More than 50 firefighters tackled an arson attack which destroyed a disused hotel.
Flames tore through the roof of the empty Cranfield Lodge Hotel in Maypole Road, East Grinstead, at 11pm on Monday.
Fire crews tried fighting the fire from inside the building but had to withdraw when flames burst through the roof and there was a risk parts of the building might collapse.
With flames leaping from the building, fire chiefs decided the only safe way to fight it was from the outside and to surround the building with hose reels and jets.
Firefighters were still at the scene damping down early yesterday. No one was hurt.
The owners brought in machinery to pull down the front of the building to make it safe.
Police were alerted to the fire at around 11pm and detectives launched an arson investigation.
Maypole Road was closed and traffic was diverted and it remained shut for most of yesterday.
Fire crews from East Grinstead, Crawley, Haywards Heath, Horsham, Horley, Burgess Hill, Steyning, Findon and Keymer were among those involved in fighting the blaze.
The fire is believed to have started on the ground and first floors, a tell-tale sign it was started deliberately.
Police and fire experts last night were sifting through debris looking for clues.
The hotel was last used as a bed and breakfast hotel and police were investigating whether squatters had broken in.
A spokeswoman said: "The fire was started probably some time between 10pm and 11pm, "It was not terribly late and we are sure people were driving by at that time.
"Someone may well have seen something they did not think important at the time but could be vital to our investigation."
Witnesses or anyone with information was urged to contact Detective Constable Annette Woodland at Mid Sussex CID on 0845 6070 999, quoting serial 1770 of 20.02.06.
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