An initial sweep of a US Navy medical centre in San Diego has found no sign of a gunman after someone reported hearing gunfire at the facility, the Navy said.

Military and local law enforcement rushed to Naval Medical Center San Diego (NMCSD) after the sound of gunfire was reported around 8am local time.

The centre was placed on lockdown and those inside were ordered to shelter in place.

Teams with dogs began sweeping Building 26, where three gunshots were reportedly heard coming from the basement, the Navy said.

"There's no evidence of a shooting right now that we know of, there was just a report of three shots heard," Navy Region Southwest spokeswoman Amanda Chavez told a news conference around 11am local time.

As authorities responded to the medical centre, NMCSD advised people at the site to "run, hide or fight".

The post on Facebook read: "ATTENTION! An active shooter has just been been reported in building #26 at Naval Medical Center San Diego."All occupants are advised to run, hide or fight."

"All occupants are advised to run, hide or fight."

San Diego police told Sky News there had been no other reports of shots fired since the initial report at 8am.However, police still described it as an "active situation".

However, police still described it as an "active situation".

Medical centre spokesman Mike Alvarez would not confirm there was an active shooter.First responders were going room by room and evacuating those inside.

First responders were going room by room and evacuating those inside.

Building 26 houses offices and barracks for wounded sailors and Marines.

Three schools in the vicinity were briefly put on lockdown as a precaution.

The San Diego Unified School District tweeted before 10am local time that the lockdown had been lifted.
"Students, staff are safe", the school district tweeted.