RESIDENTS living near a chemical plant at the centre of a huge explosion believed they were under attack from terrorists.

The blast, at the Terra Nitrogen (UK) Limited site in an industrial area off Haverton Hill Road, Billingham, Teesside, at 12.15am could be heard 20 miles away.

Residents reported hearing the huge blast and seeing a massive ball of flame.

Cleveland Police declared a major emergency after the explosion, believed to have been in a pipeline.

Two workers at the plant, injured in the blast, were taken to hospital for treatment on cuts and bruises, but were not believed to be seriously hurt.

Nearby roads were closed and residents were advised to keep their windows and doors shut as a precaution.

Nearby residents said they thought a terrorist attack was happening on their doorstep.

Mechanic Mark Sanderson, 27, who lives one mile from the plant, said: "There was a big, massive fireball going into the sky.

"It sounded like a bomb going off, I didnt know what to think, it was really quite scary."

Fellow resident Peter Honeyman said: "It seemed like the world had ended. There was a big loud bang and then a flash. It lit the sky up."

Les Gunn, who lives about four miles away from the plant, said: "I am four to five miles away from Billingham and the area of the chemical works but the noise was absolutely deafening."

The explosion caused a fire involving mixed gases including hydrogen, nitrogen and a small amount of ammonia.

Firefighters and ambulance crews were called to the scene and by 2.45am the blaze had been put out.

The plant, which produces ammonia and was previously owned by ICI, was shut down.

An investigation by the Health and Safety Executive and the Environment Agency was getting underway this morning.

Supt Ian Richards of Cleveland Police said: "Fortunately what was initially perceived as a major incident was quickly dealt with."

A spokeswoman for Cleveland Fire and Rescue Service added: "A large number of crews were sent to the incident."

A Terra Nitrogen UK spokesman said: "The incident happened on a pipe at the plant and led to a fire involving mixed gases including hydrogen, nitrogen and a small amount of ammonia which was extinguished automatically as the pipe depressurised.

"At no stage was there any danger to the public."

Terra Nitrogen is the UKs largest manufacturer of nitrogen products used extensively in the chemical industry and agriculture.

The company employs around 400 people in the UK which includes 250 people on Teesside.