DETECTIVES are keeping a vigil at the hospital bedside of a father-of-five who is suspected of starting a blaze which killed his wife and four daughters.

Mohammed Riaz, 49 - the only survivor of the fire - is said to be in a critical condition in the specialist burns unit of Wythenshawe Hospital, Manchester, suffering from serious burns and smoke inhalation.

Officers are waiting until his condition improves before questioning him about the incident.

He was rescued from the house in Tremellen Street, Accrington, by firefighters and resuscitated at the scene.

The bodies of Caneze Riaz, 39, a youth and community worker, and daughters Sayrah, 16, deputy head girl at Moorhead Sports College, Sophia, 15, Alicia, 10, and Hannah, three, were discovered upstairs in the house after fire crews broke in through a bay window at around 1.50am on Wednesday.

Two passers-by had contacted the Fire Brigade after spotting flames inside the house.

Mr Riaz's son, Adam, 17, has been told about the tragedy while in Christie Hospital, Manchester, where he is receiving treatment for leukaemia.

At a press conference at Lancashire Police headquarters in Greenbank, Blackburn, 12 hours after the fatal blaze, Detective Superintendent Mick Gradwell said: "It is our top line of inquiry to speak to someone who was in the house at the time.

"This is a murder inquiry because the fire was started deliberately.

"There is no evidence that anyone left that house. The indications are that it was contained within the family. However, at this stage I'm going to keep an open mind.

"I wouldn't want to speculate on whether or not there will be an arrest."

Det Supt Gradwell said that it was already clear that flammable substances had been used and there had been "several seats of fire" inside the house.

Although it appears to have been a member of the family who started the blaze, he said it was possible the scene could have been "staged" to imply that.

He added: "The house was secure and was locked from the inside. We are investigating many lines of inquiry and there are more than 30 police officers, staff and forensic scientists involved. But we are only 12 hours into the case and we have a lot of work to do."

Chief Superintendent David Mallaby said that rarely had he come across a tragedy of this nature. He added: "I have spoken to neighbours and the sense of loss, tragedy and disbelief is quite staggering."

News reporters from national and regional press, radio and television descended on Tremellen Street on Wednesday and Lancashire's Chief Fire Officer Peter Holland held an impromptu press conference at the scene.

He said: "The Fire Brigade did everything it possibly could to save the lives of the people in the property.

"It really is the most appalling tragedy for so many people to die in a fire. There is an awful lot of damage inside the house. All fire engines were at the house within five minutes of the call and we had the fire under control within five minutes of arriving.

"We have special equipment to get inside the house so that didn't cause us any difficulties. Firefighters receive an awful lot of training to deal with incidents such as this but even with the best possible training, when you are faced with the loss of five lives it's bound to have a personal impact on the officers.

"From a personal point of view it doesn't get any worse than this, to lose five people in a fire. We all join the fire service to save people's lives; this is an appalling, dreadful event."

Crews from Hyndburn Fire Station and subsequently Great Harwood and Blackburn attended the blaze.

A friend and work colleague of Caneze, Zeenat Begum, 24, of Hannah Street, Accrington, said: "I got a call at about 1.45am from a friend who said that her house was on fire. I rushed round and as I arrived the bodies were being carried out. Sayrah first, then Caneze, then baby Hannah, then Sophia, then Alicia. They were taken away. It did not seem real."