Sweep Of US Navy Centre After Gunfire Reported

People at the site were advised to "run, hide or fight" after someone reported hearing gunfire at the medical campus in San Diego.

A lockdown of a US Navy medical centre in San Diego has been lifted after authorities found no sign of a gunman or shooting.

Naval Medical Center San Diego (NMCSD) was locked down for nearly six hours on Tuesday after a single witness reported hearing gunshots.

Military and local law enforcement rushed to Building 26 on the sprawling campus after the report came in around 8am local time.

Naval personnel at a parking garage adjacent to Building 26

A post on the NMCSD Facebook page advised people at the site to "run, hide or fight". Everyone else was ordered to shelter-in-place.

But an hours-long sweep of the building by military police found no signs of a gunman or shots having been fired.

The medical centre is minutes from downtown San Diego

"There's no evidence of a shooting right now that we know of, there was just a report of three shots heard," Navy spokeswoman Amanda Chavez told a news conference.

A Department of Defense employee reported hearing at least three shots coming from the basement of the Building 26, officials said.

The Navy said the witness is cooperating with investigators.

The building houses offices and barracks for wounded sailors and Marines

The building, which houses offices and barracks for wounded sailors and Marines, has as many as 800 people in it on any given day.

Several people were seen being evacuated from the facility with their arms raised in the air.

The Navy said the building would remain closed while the investigation continues.

Some people inside the centre were evacuated to a nearby car park

The incident prompted the San Diego school district to briefly put three area schools on lockdown as a precaution.