Chief Superintendent Wayne Miller said: “The death of these three children is heartbreaking. Our thoughts are with their loved ones and the little girl and her mum who are in hospital fighting for their lives.
“We currently have specially-trained officers with the family to help them through this devastating time.”
He called on the suspect to “give himself up”, adding that “he knows who he is”.
“This is a fast-moving live investigation and we have a major investigation team with scores of dedicated detectives working tirelessly,” he continued.
“I want to describe what this incident is; it’s the murder, using fire, of three children and we have a three-year-old girl fighting for her life who is seriously ill.
“This will devastate this family forever and words cannot describe what they are going through. We need the public’s help to find the answers the family deserve.
“We want to make arrests as soon as possible and we appeal to local people to help us in this.”
Greater Manchester Fire and Rescue Service tweeted: “Sadly it’s been confirmed that three children have died following this morning’s house fire in Worsley, another child and a woman are in hospital in a very serious condition. This is a truly tragic incident and all our thoughts go out to the family.”
Two 16-year-old boys managed to escape the blaze before crews arrived but their condition is not known.
The incident has been referred to the Independent Police Complaints Commission because there had been “earlier incidents at the address”, police said.
Jackson Street has been closed off with large steel barriers and firefighters are still monitoring hot spots within the property,
Our thoughts are with everyone who has been impacted by this devastating fire.