The cab of the lorry caught fire

It was carrying 6,400 litres of ferric chloride, which is used to treat drinking water.

The blast in the cab of the lorry sent a cloud 2,000ft into the air, travelling toward Hereford.

The road remains closed, but police said the risk was over after the cloud reached Treherbert.

The explosion prompted ambulance crews to decontaminate the driver at the scene.

A pupil from nearby Llangatwg School at Cadoxton was treated after he complained of eye irritation following a morning journey passed the gutted lorry.

Chemical fire

A spokeswoman for Mid and West Wales Fire Service said: "The cab of the lorry caught fire and it spread to the chemical load.

"The chemical is toxic if involved in fire. It would have gone up into the air in the clouds of smoke.

They had a loudspeaker and were saying that there had been a toxic spillage

Landlord, Neil Davies

"It would make people sick if they inhaled it."

Twenty fire-fighters in four appliances were called and the Environment Agency is also looking in to the incident.

After quelling a chemical leak from the lorry with sand, police officers had used loudspeakers to advise Resolven residents to stay indoors, shutting windows and doors.

But one local man said people were out and about as normal, and he did not expect businesses to be forced to shut.

Des Davies, Mayor of Neath Port Talbot County Borough Council, lives near the site of the incident.

Under control

Mr Davies said: "I'm deeply concerned about it, but having spoken to the police I'm assured that everybody concerned has been taking the right and appropriate action.

He added that children at a local primary school were being kept inside the buildings.

"The caretaker at Clun Primary School alerted the headteacher and the children who were already at the school are being kept inside."

Police and fire-fighters were quickly on the scene and immediately closed the road to traffic.

No-one is believed to have been injured in the explosion.

A spokesman for South Wales Police said: "The fire is out and nobody has been injured.

"Emergency services are at the scene and the situation is under control."