The explosion at Mars Petcare, in Wodonga, happened about 12.20am as thousands of single-serve trays of cat food were being cooked inside the pressure cooker.

The company’s corporate affairs manager, Duncan Hall, said 18 workers were nearby at the time of the blast but nobody was struck by the door or food containers.

“Our first concern was for the health and safety of the contractors; the force of the explosion was very substantial in as much as a couple of our colleagues lost their footing at the time and the distress of being near such an explosion is such that there is a fair bit of shock,” Mr Hall said.

Three men were driven to Wodonga hospital for assessment before returning to work.

The cause of the blast is unclear but Wodonga site manager Nigel Harrison said the affected plant had been shut down, with Worksafe Victoria officials at the scene for several hours early yesterday.

“Our investigations are continuing, however, at this early stage we can advise that it was a failure of a door seal and the door forcibly blew off under pressure during processing,” Mr Harrison said.

The single-serve factory, which opened in late 2006, operates 24 hours a day with up to 10,000 trays of raw meat cooked inside the 85-100 gram containers in each pressure cooker for 90 minutes.

Mr Hall said up to 400,000 single-serve cat and dog food units were produced at the plant each day, with two million processed each week.

There is a quick turnaround on the products between processing and delivery to shops, however Mr Hall was reluctant to comment on how a shutdown would affect supplies.

“We recognise that we need to provide support services for our associates, we recognise then that we need to also notify our customers but right now our focus is on making sure everyone is OK,” Mr Hall said.

Mr Hall could not say how long the single-serve plant would be closed but he said workers would be redeployed to the cannery and other areas of the business while the investigation was undertaken.

Counselling services have also been offered to employees who witnessed the large blast.