Eleven firefighters have been injured in an explosion at a hash oil manufacturer in Los Angeles.

The fire crews had gone inside the complex in the city’s Toy District after an initial report of a fire, but then had to run for their lives when a ball of flames exploded out of the building and scorched a fire engine across the street.

Some of the firefighters escaped with minor injuries but others were more seriously burned, and three are said to be in a critical condition. All those injured are expected to survive.

Los Angeles fire chief Ralph Terrazas said one of the firefighters inside the building felt things did not seem right – the pressure from the smoke and heat coming from the rear of the building were increasing.

He directed everyone to get out, and as they quickly started exiting the building it was rocked by the explosion.

Los Angeles Fire Department captain Erik Scott said “one significant explosion” occurred at around 6.30pm local time on Saturday.

Los Angeles Explosion
Huge plumes of smoke rose into the air amid the fire in central LA (Ringo HW Chiu/AP)

Firefighters inside had to run through a wall of flames he estimated to be 30ft high and wide, and those on the roof scrambled down a ladder that was engulfed in fire.

He said people at the scene described the explosion as sounding like a freight train or jet engine.

The fleeing firefighters tore off their protective equipment that had burned and helmets that had melted, Mr Scott said.

“The was one of the worst scenes I’ve seen,” he said.

Los Angeles Explosion
About 200 firefighters attended the scene on Saturday evening (Ringo HW Chiu/AP)

More than 200 firefighters rushed to the scene, as the flames spread to several nearby buildings.

Mr Scott said the building was a warehouse for SmokeTokes, which he described as a maker of “butane honey oil”.

Butane is an odourless gas that easily ignites, and it is used in the process to extract the high-inducing chemical THC from cannabis plants to create a highly potent concentrate also known as hash oil. The oil is used in vape pens, edibles, waxes and other products.

On its website, SmokeTokes advertises a wide variety of products including “puff bars”, pipes, “dab” tools, vaporisers, “torches and butane”, and cartridges.