One person remains unaccounted for, at least one building has been destroyed and a major incident was declared after an explosion at an industrial estate in South Wales.

Flames and smoke were seen after a fire broke out at Rizla House on Severn Road, Treforest Industrial Estate, at around 7pm on Wednesday.

The two-storey building was “totally alight” and “at risk of collapse”, South Wales Fire and Rescue Service said.

Three people were treated at the scene before they were discharged, a Welsh Ambulance Service spokesperson said.

Local NHS emergency departments were on “high alert” after the blaze, with people asked not to attend A&E unless “absolutely necessary”.

There are no reports of any serious injuries, however, one person remains unaccounted for, South Wales Police said.

Landlord of Rizla House Richard Hayward, 72, said there was a “severe explosion” on the ground floor of the 60,000 square foot property, which he said he has had for a decade.

Mr Hayward said one of his 13 tenants at the building restored cars, while it also contained a towel supplier and gym.

He said: “We’ve been up there for three hours, lots of police, lots of fire engines.

“The police won’t let us go anywhere near the building at the moment, it was still on fire less than three quarters of an hour ago – the police can’t tell us anything really at the moment.

“We’ve checked with every tenant that we could and all the ones we spoke to evacuated.

“It appears as though the fire started in one of the lower units there, we don’t know which one – there was a severe explosion.

“From what we can glean from various people, the fire brigade being one, the building has been destroyed… I suspect it’s probably going to look a bit like a hulk when we eventually get into it.

“The fire is still blazing and I don’t think that they think that they’re going to get the fire out much before the morning.”

He said the building used to produce Rizla cigarette papers and was built in the 1920s before being extended in the 1940s and ’50s.

Significant road closures remain in place and the public is requested to avoid the area.

Deputy chief fire officer Dewi Rose said: “At 7.05pm this evening South Wales Fire and Rescue Service (SWFRS) responded to 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.”

Tattoo artist Lucy Artiss, 40, who works at Sixteen Circles in Rizla House on Treforest Industrial Estate, said: “What I know is the explosion destroyed the entrance. Our tattoo shop is destroyed, as well as the gym.

“I left just before it happened so I didn’t witness it.”

Ms Artiss, who said her co-worker, his client and gym staff “all managed to get out of the fire exit”, added: “It was a lovely place, had a wonderful family feel to it. I’m gutted to have lost that.”

Integer Telecom, a telecommunication provider, said in a Facebook post its building was destroyed in the explosion, adding: “All our staff are safe and unharmed and business will resume as normal.”

Cwm Taf Morgannwg University Health Board said: “Due to the ongoing incident at Treforest Industrial Estate this evening, all of our emergency departments are currently on high alert.

Emergency services at the scene at Severn Road, Treforest, following an explosion at an industrial estate
Emergency services at the scene at Severn Road, Treforest (@Jo_Reggelt/PA)

“Please help us by not attending A&E unless absolutely necessary. We need to be able to provide care to those who need it the most.”

It later said emergency services were standing down from the high alert.

Jonny Foxhall, 36, the owner of nearby music venue Green Rooms, told the PA news agency: “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.”

A Welsh Ambulance Service spokesperson said 10 emergency ambulances, seven rapid response vehicles and the Hazardous Area Response Team were sent to the scene.

Emergency services remained at the scene of the blaze overnight.

Residents living nearby were advised to close all doors and windows while the incident continues.