An active shooter and three gunshots were reported at a US Naval Medical Centre in San Diego on Wednesday, triggering a heavy law enforcement response.

Officials have since stated there was no sign of a shooting and no reports of deaths or injuries.

"There’s no evidence of a shooting right now that we know of, there was just a report of three shots heard," said Navy Region Southwest spokeswoman Amanda Chavez.

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Workers from the building were seen coming out in a single-file line with their hands raised in the air. Photo: Twitter/NelCepeda

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Gate at Naval Medical centre is San Diego has been blocked due to report of active shooter. Photo: NBC 7/Twitter

A male witness earlier reported hearing three shots in the basement of a building housing a gym and barracks at the medical centre around 8am local time.

Authorities are now interviewing the witness, but believe it may have been an innocent mistake and not a hoax.

Military police were talking to the person who reported the shots fired, Chavez said.

First responders and Navy working dog units could be seen clearing the building where the shots were heard, the Navy statement said, adding that the medical centre was on lockdown and a shelter-in-place order had been given.

Workers from the building were seen coming out in a single-file line with their hands raised in the air, as heavily armed police maintained a perimeter around the site.

The San Diego County Sheriff's Department sent an armoured van and a 12-officer SWAT team to assist military police in clearing the building.

Navy Captain Curt Jones, asked about the status of the situation, said, "I would say we're pursuing the information we have and ensuring that everyone is safe."

A post on the medical centre's Facebook page had earlier advised occupants to "run, hide or fight," the protocol advised by the US Department of Homeland Security in response to an active shooter.

All non-emergency response staff were asked to stay away from the compound. The shooter was reported in building #26, the post mentioned.

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