THERE are fears a casualty could be trapped in the rubble of a gym after a fireball "explosion" ripped through an industrial estate.
One person remains "unaccounted for" after the explosion at the Treforest estate in South Wales last night.
Emergency services closed roads while they battled the blaze.
Crews said around midday that the fire was mostly extinguished, but they were still fighting "small pockets of fire".
Experts are still working to determine the cause of the blaze.
All major hospitals in South Wales were put on "major incident alert", with locals urged to stay away unless seriously injured or ill - but this alert was later lifted.
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More than 10 police and fire service vehicles were spotted at the scene after neighbours said they heard a loud bang before the huge fire broke out.
A gym, dance studio and at least one car dealership on the industrial estate are all understood to have been affected by the explosion.
Posting on Facebook, business owner Lucy Artiss said: "My tattoo shop and gym just exploded.
"Lost everything but thankfully not hurt. I feel numb, to be honest.
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"That gym was my favourite place. Looks like I'll need to find a new shop.
"So gutted but hey, everything will be replaced. It is what it is."
It is not yet known what the cause of the explosion was.
Late last night Deputy Chief Fire Officer Dewi Rose said: "At 7.05pm this evening SWFRS responded to a number of repeat calls about an explosion at Mindset Gym, Rizla House, Severn Road on Treforest Industrial Estate, Pontypridd.
"SWFRS currently has 16 pumping appliances, a number of special appliances and officers in attendance.
"The latest from the scene is that the building, a large multi-use two-storey commercial premises, is totally alight and at risk of collapse.
"Our partners from South Wales Police, WAST, Wales & West Utilities, NRW, RCTCBC, CTMUHB and National Grid are supporting us to deal with the incident.
"At the moment our focus is firmly fixed on the emergency response."
Local councillor Karl Johnson told Sky News that the explosion happened near the premises of Mindset Functional Fitness Ltd.
He added that the front of the gym building was "completely destroyed" and that a nearby car dealership had also been damaged.
South Wales Police said roads around the industrial estate would stay closed for some time following a "serious incident".
The force said: "We are at the scene of a serious incident on Severn Road, Treforest.
"The roads around the Industrial Estate are currently closed and are expected to remain as such for some time.
"Please avoid the area. Updates will be provided when available and appropriate."
More than 15 police cars, 10 ambulances and several fire engines are understood to have scrambled to the scene.
Yesterday the Welsh Ambulance Service said: "Tonight we have declared a major incident in response to a large fire at Treforest Industrial Estate, Severn Road, Pontypridd.
"We have sent 10 emergency ambulances, seven rapid response vehicles and the Hazardous Area Response Team to the scene.
"We have been supported by the Emergency Medical Retrieval and Transfer Service."
Posting on Facebook, one resident said: "My house was rattling, must have been a big explosion."
South Wales radio station GTFM said: "We have received a report from a listener in Upper Boat of a loud explosion which seems to have triggered a large fire."
Jonny Foxhall, 36, who owns a nearby music venue, said: "Our front door was flung open so we went out to see what had happened.
"We could see a smoke cloud and an orange glow from above the treeline quickly followed by flames."
He added: "To feel the shockwave from the explosion is something I've never experienced before."
One Facebook used claimed they could see the blaze from their flat in Cardiff.
Locals have been warned not to visit A&E in the area unless "absolutely necessary".
Swansea Bay NHS said: "Because of the explosion & fire in Treforest, all major hospitals in S. Wales including Morriston are on major incident alert.
"Avoid Morriston unless you have a very serious illness or injury."
Rhondda Cynon Taf Council said: "Please stay away from the Power Station Hill area to ensure emergency services can carry out their duties unobstructed and to keep yourself safe."
Stagecoach South Wales said its 132 and 120 services were unable to serve Rhydfelin and Hawthorn on their return journey due to the explosion.
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RSD Gym Dance & Cheer said that it had closed to keep its members safe.
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