A man and a woman in their 20s have died and their two children are in hospital after a fire ripped through their home in Blackpool.
Lancashire Police launched a joint investigation on Wednesday morning.
Speaking at a press conference at the scene of the fatal blaze on Peter Street, Chief Supt Mike Gladwin, West Divisional Commander for Lancashire Police said the two victims were the parents of the injured children.
Supt Gladwin told reporters: “We understand they lived in the property and are the parents and their children.
“We have evacuated a small number of properties while we conduct our investigations.”
Officers were called to Peter Street at 2.39am following reports of a fire with people reported to be inside the property.
There was a significant emergency response involving officers and the Lancashire Fire and Rescue Service.
“Tragically, a woman in her 20s was found deceased at the scene. A man in his 20s was later pronounced deceased at Blackpool Victoria Hospital,” the force said.
“Our thoughts are with their loved ones at this devastating time.
“Two children have been taken to hospital for treatment. One of them is in a very poorly condition.
“Work is ongoing with our colleagues from the fire service to establish the cause of the fire. We are keeping an open mind at this stage.”
Nobody has been arrested.
Mr Gladwin said: “This incident has resulted in two people losing their lives and my thoughts are with their loved ones at this extremely distressing time.
“I know this tragic news will be met with great sadness in the local community and people will want instant answers.
“However, there are grieving loved ones still trying to come to terms with this devastating news. With that in mind, I would ask for patience and that people avoid unhelpful and upsetting speculation.”