The blast, which was reportedly caused by a cylinder of liquid nitrogen, left one man injured and a shed badly damaged on Tuesday.

A spokesperson for Camlin Transport, a specialist transportation service which operates across the country from its Tamworth depot, did not answer a number of questions sent by the Leader, including whether it was doing inventory on its remaining fleet.

Nor did the spokesperson identify when the site would be reopened.

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"Normal loading and transport processes were followed. Camlin is committed to providing a safe and professional environment for all their employees, clients and the community, on and off the road," the spokesperson said.

"The focus now is on the investigation, and we are continuing to operate the business."

A spokesperson for SafeWork NSW said the regulator had started a "preliminary investigation of the cause" of the explosion on Tuesday.

According to its website Camlin has operated across the country for over 30 years and has vehicles based in Sydney, Melbourne, Adelaide and Brisbane.

It specialises in the delivery of cryogenic gases including argon, oxygen, CO2, nitrogen, hydrogen and helium.

A shed in the depot was badly damaged in an explosion which could be heard as far away as East Tamworth.

According to Fire and Rescue NSW, the blast was caused by a fault in a pressure relief valve of an 18,000-litre cylinder, which over-pressurised, causing a blast which sent debris up to 100 metres away.

Paramedics treated an employee on scene for injuries suffered in the blast, which the company described as "minor cuts and abrasions".

After waiting several hours for the all-clear to approach, firefighters vented three remaining liquid nitrogen cylinders on Tuesday night.

Tamworth Regional Livestock Exchange Manager Steve Davidge was just 500 metres away when the explosion occurred.

He was on the phone at the time, he said.

"This almighty bang went off..." he said.

"Obviously I knew that this gas place down here must have done something."

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