The blast hit Harford Attachment’s plant in Hellesdon where the firm makes excavator buckets and quick hitches.

Norfolk Police said: “Two men, one aged in his 50s and the other in his 20s, were sadly pronounced dead at the scene.

“Both men, who were employees, were found within a room inside the building. No one else was injured.”

Fire crews and the air ambulance were also called to the scene.

Ashley Cashfield, who works at a nearby building, told the BBC he saw “very thick, black plumes of smoke rising quite slowly” from Harford Attachments, before the emergency services arrived.

“It didn’t look very nice at all,” he said. “There was lots of panic in people’s eyes.”