Two of them suffered smoke inhalation and were taken to Bedford Hospital South Wing, while a third sustained leg injuries and was airlifted to Addenbrooke's Hospital.

The blaze on Redwood Grove was so intense that it led to the collapse of the building's roof.

The firefighter was one of those who suffered smoke inhalation, said the East of England Ambulance Service, as fire teams described the blaze as a "major incident".

A local resident said they saw one person leap from a second-floor window to escape the burning block.

Pictures from the scene showed the three-storey structure on fire, and an adjacent building was evacuated.

Emergency services warned people to stay indoors and keep their windows and doors closed.

A spokesperson for Bedfordshire Fire and Rescue Service said: "We are currently in attendance at a major gas explosion on Redwood Grove, Bedford.

"There are currently six appliances, two water carriers, an incident command unit at the scene. Please avoid the area and keep windows and doors closed."

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A statement from Bedfordshire Police earlier said: "Emergency services have responded to an explosion at Redwood Grove, Bedford this morning.

"This resulted in a significant fire at a three-storey block of 20 flats, which has engulfed the whole building and caused a large portion of the roof to collapse."

'I witnessed someone jump from the second-floor window'

Adam Fisher, who works in a nearby building, said: "A huge explosion [was] heard - everyone went to our work car park to see what was happening.

"Our building is adjacent to the apartment complex - immediately an inferno (was) visible, huge smoke cloud billowing, people screaming and people frantically calling for emergency services."

Another witness, who did not want to be named, said: "I walked to town and saw the flames and also witnessed someone jump from the second-floor window whilst flames were blaring out."

Bali Mummon told Sky News: "You just kind of felt helpless at the time, thinking of the worst.

"The hope is people were not seriously injured - or even fatalities.

"And I don't know what's happened but I just hope there was hardly anyone in there."

John O'Reilly, 76, was "knocked off [his] feet" by the explosion.

He added: "There were bricks in the road so it was obviously a very large explosion to do that sort of damage."

The nearby John Bunyan Centre was set up as an emergency assistance centre, with members of the British Red Cross present to help.

Around 20 people were at the site by 2pm, said Sarah Stevens, manager for community safety and resilience for Bedford Borough Council.

She said the "majority" of people had "gone to friends and family so they're safe and settled".