A child has died after a massive explosion wrecked a house in the Shaw area of Oldham, police said.
Another individual is trapped and a third is unaccounted for.
Emergency services are at the scene of the incident, which has affected a number of terraced properties.
A spokeswoman for the North West Ambulance Service said one patient had been taken by helicopter to Wythenshawe Hospital in Manchester with 80% burns.
The explosion is thought to have been caused by a gas leak.
Emergency services described the explosion as "very serious".
Superintendent Neil Evans of Greater Manchester Police told reporters at the scene that the child had been confirmed dead.
Supt Evans said: "This is an ongoing search and rescue effort and we are offering our full support to the fire and other emergency services."
He added: "Our main and immediate focus right now is to assist in ensuring those injured in the explosion get any medical assistance that they need."
The spokeswoman for the North West Ambulance Service added: "We are currently assessing the scene and working closely with other members of the emergency services, with our priority being to ensure people receive the medical help they need as quickly as possible."
In a statement, Greater Manchester Fire and Rescue Service said: "One man has been rescued following a possible gas explosion in Shaw in Oldham."
"The control room has received numerous calls from members of the public and the initial information from the public is that it involves a number of terraced properties in Duchess Street with possibly people trapped."
Steve McGuirk, chief fire officer for Greater Manchester, said in a tweet: "Just had an update on the incident in Oldham - very serious, we have crews and search and rescue teams on scene working hard."
Greater Manchester Fire Service said more than 30 firefighters were at the scene carrying out a search of the immediate area.
Those involved included specialist search and rescue teams, with a dog, and colleagues from Lancashire Fire Service.
Alex Perkins, who lives on Buckley Street, told the BBC: "It's like a war zone - tiles that have blown off literally across the streets, there's just debris everywhere."
"It's just empty, there's nothing there, just bricks on the floor, just rubble."
Georgian Ulla, who lives on Buckley Street, added: "All the lights shook - I thought someone was breaking in to begin with.
"First thing that I saw was all the toys on the floor. Apparently there are kids that live in the house."
Shaw ward councillor Mark Alcock, who lives a quarter of a mile away, said: "An end-terrace house has been completely flattened and properties up to 800 metres away have had their windows blown in. It's a real mess."
Superintendent Neil Evans of Greater Manchester Police confirmed a child had died in the explosion, a further victim was in hospital with 80% burns, another male unaccounted for and a fourth person trapped.
"One individual we can see, we are trying to remove debris to get that person out," he added.
No further information has been given on any of the four people involved in the explosion.
Mr Evans said gas was "one element" the investigation will focus on.
In a statement, National Grid confirmed that it received a report of a smell of gas in the Edmund Street and Buckley Street area of Shaw at 10.40am today.
It added: "This was shortly followed by another call to report that there had been an explosion.
"Engineers arrived on site to find that five properties (no 7 to 13 Buckley Street) had been badly damaged."
"So far, NG engineers have been unable to get into these properties to conduct an investigation but the gas mains in Buckley Street and Chancery Lane have been cut off for safety.
"Around 100 homes in the area have been evacuated."
A police spokesman at the scene told the BBC: "There's one individual the fire service can see. They are trying to remove the debris to get that individual out."
He said it was a search and rescue operation. "The priority is to preserve life and prevent further injury."
The council said several roads were closed including Crompton Way, which is closed from the junction of Rochdale Road to Linney Lane. Rochdale Road is closed between Beal Lane and Linney Lane.
Buckley St, Oak St and Edmund St are also closed, the council said.
The scene centres on a house near Buckley Street and Duchess Street in the Shaw area of Oldham.
The property was destroyed and a number of others were wrecked in the blast.
The explosion reduced three terrace houses to rubble.
According to locals, the man seriously injured is named Anthony Williamson and lives at one of the rented properties with his partner, mother-of-six Tanya Williamson.