Residents reported hearing loud bangs and seeing fireballs as a dramatic blaze at a plastics factory sent plumes of smoke billowing into the sky.
Up to 10 pumps had to be called in to fight a fire, with the smoke visible across much of Bradford.
Shortly after the fire broke out at Moulds, Patterns and Models Ltd, a factory on Swinnow Lane, Bramley, a spokesperson for the West Yorkshire Fire and Rescue Service said: “Firefighters are in attendance at a fire at a plastics factory on Anchor Works in Swinnow Lane, Bramley.
"We received several calls at around 12noon Monday to the incident. Crews in attendance came from Stanningley, Leeds and Rawdon along with two engines from Bradford.
"Due to the large amount of smoke in the area we are advising people to keep windows and doors closed and also to avoid the area if possible."
Smoke was billowing up into the sky and was visible from miles away in Bradford.
Dramatic photographs taken on the Stanningley Bypass showed thick smoke from the fire blowing across the road and reducing visibility.
One nearby resident was understandably shaken by the incident.
As she stood on a bridge overlooking the huge blaze, she told the T&A: "There were just thick black plumes of smoke and then explosion after explosion, then obviously the emergency services came really quick.
"I live two doors down and it was quite frightening because you don’t know what’s happening. It was thick black smoke.”
One man who lives nearby said he saw gas cylinders blow up.
"It was just like fireworks night," he said.
"There were workers just running down. All you could hear was these big bangs.
"When I came out I saw all the smoke. All you could see was these gas cylinders blowing up and going up in the air."
Describing what the sound was like, he said: "Like a bomb. There's quite a lot of fire engines, a lot of ambulances, lots of police.
"The smoke was that bad cars couldn't see because of the black smoke. I've never seen smoke that black before. When I got there there was another explosion. We saw these massive fire bubbles go up in the air."
One nearby resident, who lives on Swinnow Drive about 300 metres from the fire, said: "My back garden looks straight over to the plastics factory.
"I heard what sounded like bangs and detonations which woke me up at 11.30am," he said. "Whatever it was it sounded likes it was combusting all at once.
"I heard what sounded a gunshot screaming and felt a shockwave in the house.
"The smoke was pitch black and at one point I saw a fireball.
"It smells awful. You can definitely tell it's from a plastics factory."
One family reported seeing a big orange ball of fire.
The woman said: "I saw this black smoke. It was really thick. You couldn't see where you're driving down the bypass, they had to slow down."
One dad said his daughter was in the garden when the fire broke out. She alerted her father that something might be on fire.
"It was horrendous," he said. "You could smell it."
He received an email from his son's school saying classes were in lockdown due to a chemical fire.
"We got an email saying the school was in lockdown," he said.
"We went to have a look and just saw a massive fireball and things getting blown into the sky.
"It was pretty scary."
Two nearby schools were unaffected by the fire or smoke.
A spokesperson for Stanningley Primary School, on Leeds and Bradford Road, Stanningley, said: "It hasn't affected us at all. We were in close proximity, less than half a mile away, but luckily the wind was in the wrong direction.
"There wasn't even a whiff of smoke. If you hadn't seen it, you wouldn't know any difference."
A spokesperson for Park Spring Primary School, on Swinnow Lane, added: "It didn't affect our school at all. You could see all the smoke, but it was just a talking point at lunchtime."
A fire service spokesperson said at mid-afternoon Monday: "We're just damping down now, but the fire is ongoing and we have two pumps in attendance.
"We had 10 pumps at the scene as of 2.15pm but just two there now. We don't know what the cause of the fire yet."
The fire closed a number of roads in the area including the Stanningley Bypass.
West Yorkshire Police said road closures were in place around the site and the A647 Ring Road is closed between Dawsons Corner and the Wickes roundabout.
The fire also disrupted bus services in the area.
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