LONDON - A fire which gutted a hotel in Cornwall last summer leaving three people dead was started deliberately and is now being treated as murder, police said on Tuesday.

Teacher Peter Hughes, 43, his mother Monica, 86, and Joan Harper, 80, all from Staffordshire, were killed in the fire that destroyed the Penhallow Hotel in the holiday resort of Newquay.

Detective Chief Superintendent Chris Boarland of Devon and Cornwall Police said a five-month inquiry including fire experts had ruled that arson was to blame.

"This force and the experts can come to no other conclusion than that this fire was started deliberately," he told reporters.

"The fire at the Penhallow Hotel is therefore now officially classified as a murder investigation.

"What I'm saying to you is the deaths of Joan Harper, Peter Hughes and Monica Hughes occurred as a deliberate act of someone or some people in causing that fire."

He said the fire last August had been the most serious hotel blaze in the country for 30 years, adding it was an "absolute miracle" that none of the other 86 residents, many of whom were elderly, was killed.

More than 100 firefighters battled to control the blaze which engulfed the building late on a Saturday night, fanned by high winds.

Pat Albutt, brother of Peter Hughes and Monica Hughes's daughter, said her family felt "like the heart has been ripped out".

Her brother died after falling from a window on an upper floor of the tall hotel, which formed part of an Edwardian-era terrace. He had been trying to save his mother's life.

"My dad used to say taking someone's life is an ultimate theft," she said.

"You are taking everything there is from them and taking so much from the people who are left. I would be so grateful if anyone could come forward and give us some answers as to how and why this happened."

DCS Boarland appealed to anyone locally or who had been on holiday in the area at the time who might know anything about the fire to come forward with details.

"If there is any information at all, it is crucial that they contact us because it just might be that little piece of the jigsaw that we need to detect this really horrible crime," he said.

"For me it's unlikely that somebody hasn't spoken about this at some point."