Four people are this afternoon being hunted by police after a suspected arson attack at a recycling plant in Moxley, which sent smoke containing asbestos across the Black Country.

Police want to talk to four people seen near AWM Recycling Ltd shortly before the fire broke out.

An unlocked door was discovered at the rear of the property, in Western Way. Officers want to speak to two people in dark clothing who were seen acting suspiciously at the back of the site between 1am and 3.45am yesterday. A man and a woman spotted near the factory in the early hours are also being hunted.

It can also be revealed today the recycling plant was under investigation by a Government agency.

The Environment Agency had visited the business two days before the fire to “ensure that all the activities on the site are legal”.

Up to 100 firefighters tackled the fire at its height after it broke out at 4am yesterday at the centre, which recycled plastics.

Crews were still on the site today investigating the cause of the blaze and making sure the area is safe.

Up to 80 residents were evacuated from their homes and were only allowed to return some 12 hours later at around 4pm yesterday. Health warnings have been issued today after it emerged asbestos was contained in the roof of the building and was stored on site. Residents have been urged to keep doors and windows closed.

It has also emerged the firm, which had three sites across the Black Country, ceased operation at its Coseley base just days ago.

Solicitor for the landlords of the Budden Road site, Charles Fraser-Macnamara, today said: “The landlords of the site have repossessed it.”

It has a third premises in Chillington, Horseley Fields, Wolverhampton, which is still open, but staff there refused to comment on the fire or the company’s business. The Environment Agency confirmed it began its probe on Monday and entered the site using powers under the Police and Criminal Evidence Act. The nature of the investigation is not known.

Lyn Fraley, spokeswoman for the Environment Agency, said: “Due to the company’s current issues, we have been checking to ensure that all the activities on the site are legal. On Monday, we served a routine Code B Notice under the Police and Criminal Evidence Act to assist in our inquiries. The investigation is continuing.

“For clarification, the major issue regarding asbestos in this fire is the asbestos contained within the roofing fabric of the building. Although we have not yet been able to go on site to check, we have no reason to believe that the small quantity of waste asbestos on site was involved in the fire.”

Simon Johnson, process manager at AWM Group, today refused to comment on the closure of the company’s site in Coseley. But he said the Environment Agency had been “happy with what we were doing”.