Homes were evacuated and 40 firefighters called in to deal with a massive blaze in a house under construction in Launceston Road, Callington early on Wednesday morning.

The evacuees were awoken by police shortly after 4am and were taken to the nearby Ginsters factory where staff looked after them and provided refreshments.

The fire is thought to have been started deliberately and police have issued an appeal for witnesses and for information about a man seen in the area around the time the fire broke out.

A total of 24 people including Callington's Portreeve (mayor), Rick Lumley and his family, had to be woken and asked to leave their homes as firefighters from Callington, Saltash, Liskeard and St Austell fought to contain the fire raging through the three-storey timber framed building.

The house was destroyed and is expected to have to be demolished, while an adjoining property also under construction was also affected, although a fire brigade spokesman said later the damage there was 'superficial'.

The fire was spotted at about 3.40am by police officers on routine patrol but by then the house, opposite Callington Community College, was well ablaze.

Sue Lumley, wife of Portreeve Rick, said the first she knew of the drama next door to their home was when she and her husband, together with their two daughters, were woken by police at about 4.10am and asked to leave and go to Ginsters.

'The house was well ablaze by then,' she said. 'We went to Ginsters and they looked after us and our neighbours very well.'

She said they were eventually allowed to return home and were relieved to find it was undamaged, although the heat, which had been tremendous, had buckled some of the UPVC panes in their greenhouse. 'The firemen were brilliant and were still damping down our shed and garage, from which they had removed some gas cylinders – our main job then was making them cups of tea.'

At nearby Callington Community College lessons were unaffected by the fire earlier in the morning although staff and buses delivering children had to make short diversions to avoid fire crews who were still at work damping down the wrecked building.

Police are anxious to identify a man who was seen acting suspiciously at the scene of the fire. A spokesman said cleaners at Callington College spotted a man acting suspiciously in the area at about 3am.

He was wearing a beige top which was possibly a hoodie.

Anyone who may have information regarding the fire or the man is asked to contact the police on 08452 777 444