OHIO (REUTERS) - Wright-Patterson Air Force base in Ohio has lifted a lockdown that was imposed late on Thursday (Sept 9) after reports of an active shooter at the National Air and Space Intelligence Centre of the base.

"Wright-Patterson Air Force Base has given the all-clear. Lockdown has been lifted. When more information is available, we will share it here," 88th Air Base Wing said in a tweet early on Friday.

No injuries were reported and no evidence of gunshots had been found, base spokesman Bob Purtiman told WDTN TV channel, a local affiliate of NBC, adding that the report of the threat was "credible".

The spokesman said two people had reported hearing gunshots in the area, leading to a series of sweeps in the centre's 850,000 sq ft building until early on Friday.

The National Air and Space Intelligence Centre serves as the US Department of Defence's main source of analysis for foreign air and space threats, according to its website.

The lockdown was lifted over four hours after the initial alert. The base responded by carrying security sweeps in the area.

Wright State University, which is located next to the site in Dayton in western Ohio, had advised students and employees to stay clear of areas towards the north end of its campus.