A power plant using farm waste today exploded at Harper Adams University, spilling tonnes of slurry.

A 200-metre exclusion zone was today put in place by police, who described it as a "chemical incident".

It is the second time the £3 million anaerobic digestion plant has leaked sludge across land in Edgmond, near Newport.

The last pollution scare came in February 2013 when thousands of litres of waste flooded farmland and entered nearby rivers.

Today's explosion, which destroyed a large processing tank, happened in the early hours. The scene was sealed off and Shrewsbury Road was closed as firefighters, police and officials attended the scene.

The university said it could not say how much waste had leaked out of the tank. It has left land next to the plant waterlogged and brown slime has poured out over a nearby track. Environment Agency inspectors were today at the site assessing the impact of the explosion.

Dr David Llewellyn, vice-chancellor at Harper Adams, said: "We will be taking all possible steps to minimise impact on the surrounding environment. Students taking exams have been alerted about the road closure."

The plant was built in 2011 and takes food and waste to create power.

Today's apparent blow out of a processing tank is thought to have happened in the early hours of the morning, on a different area to last year's drama.

An onlooker, who did not wish to be named, said: "The plant is made up of about six main structures and one, a 30ft high corrugated metal building at the back of the plant, has had virtually all of one side apparently blown out.

"There is a huge mountain of slurry piled up inside which has poured from the building onto a farm track and part of the roof has collapsed."

The university said it could not say how much waste had leaked out of the tank, which is situated about half a mile from the main university buildings.

The spillage has left land next to the plant waterlogged and brown slime has poured out over a farm track.

University and Environment Agency officials are today at the site assessing the damage and working to minimise the effect on the environment.

Fire crews and police arrived at the scene at around 10am and sealed the scene off with tape, while the buildings were inspected.

Dr David Llewellyn, vice-chancellor at Harper Adams, said none of the waste had reached Shrewsbury Road, which police had closed to allow the clean up to progress unhindered.

He said: "Business will continue as normal elsewhere. Students have been alerted to the road closure to allow them to take alternative routes and give themselves plenty of time to reach the campus for end of year exams."

The £3 million power plant, which uses up to 11,000 tonnes of dairy and pig slurry and 12,000 tonnes of food waste, last hit the headlines when it sprang a leak in February 2013.

The first drama saw thousands of litres of waste flood farmland and entered nearby rivers, prompting a major clean-up operation.

The storage tank which leaked in February 2013 was not sealed off until 36 hours later, by which time tonnes of farm waste had leaked sparking a pollution scare around the site.

Then, thousands of litres of processed farm waste spilt out over farmland and entered the local watercourse which feeds into the rivers Strine and Tern.

A bund built to contain any leaks failed and the digestate – a by-product from the renewable energy process – flowed in to a nearby field, the Environment Agency said at the time.

Temporary dams were put up to stop more pollution flowing in to watercourses, though a significant amount did get in initially. Environment Agency staff also added hydrogen peroxide to the water at the meeting point of the Rivers Strine and Tern in a bid to help wildlife alongside the waterourse to survive.

They also worked with Severn Trent Water and Telford & Wrekin Council to ensure drinking water was not affected, although pollution experts said there was no risk of waste from the tank entering the town's water supply.

There were no reports of any serious environmental impacts after the February 2013 leak.

The £3 million anaerobic digestion plant was built in 2011 in a bid to offset campus carbon emissions and has saved 3.4 times the current emissions from campus buildings.

The plant takes food and farm waste and creates power to be used on campus.

The facility was developed through a partnership between Harper Adams, Biogen Greenfinch and E.ON.