Stockton residents were left rattled on Thursday night following a series of explosions as "loud as the Fort Scratchley cannons", resulting from an unplanned shutdown of Orica's ammonia plant.
Startled residents reported four or five explosions coming from the Kooragang Island facility shortly after 11pm.
Fire and Rescue NSW attended the site in response to community concerns.
An Orica spokeswoman confirmed the plant was shut down for unplanned maintenance to address a minor pipe leak.
"While shutting down, two steam pressure relief valves operated in accordance with their design to maintain safe pressure in the system," she said.
"Unfortunately, the steam venting process created noise, which resulted in a number of community complaints.
The spokeswoman said there was no risk to the community or environment.
The company, which self-reported the incident to the Environment Protection Authority, has apologised for the incident.
"We acknowledge that the noise caused concern for some community members and we sincerely apologise for any distress or inconvenience," the spokeswoman said.
"We encourage affected community members to contact us via our hotline 1800 789 044 if they require any further information."
An EPA spokeswoman said the authority had requested Orica provide more information about the incident.
Stockton Community Group member Keith Craig was among those who heard the explosions.
"It was concerning. I'd say it was as loud as the Fort Scratchley cannons," he said.
"There was a 'boom' and then it went on for a bit," he said.
Another Stockton resident Ian Taggart said the incident should be classified as a "near miss".
"Reliance on any "last line" safety measure is never part of standard and acceptable operating practice by any company," he said.
"Had those safely valves failed God know what might have happened."
The Kooragang plant has been incident free since an infamous hexavalent chromium leak in 2011 resulted in the chemical being sprayed over homes in Stockton.
Under a proposal, facilities would need to comply with new standard separation distances from populated areas and infrastructure in order to be licensed to store ammonium nitrate.
While the proposal is welcomed by residents, the Orica and the coal industry argue the rules would increase the risk to the public by dramatically increasing the amount of product coming through the Port of Newcastle.
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