US base lockdown lifted in South Korea
US Osan Air Base lockdown lifted in South Korea as no shooter was foundLee Jae Won/Reuters file photo

A brief lockdown of the US Osan Air Base in South Korea has been lifted after no shooter was found.

The base was locked down following reports of a suspected shooter in a high school on the base, but officials have not found anything suspicious following a thorough sweep.

"Osan American High School, Middle School and Elementary School are on lockdown here, along with the entire installation following reports of an active shooter in the location of the school," the 51st Fighter Wing Public Affairs of the Osan Air Base said on its website.

Residents of the base were earlier told to stay indoors until further notice as the lockdown was on.

The Osan Air Base, located south of capital Seoul, houses about 28,000 troops which are stationed in South Korea.

The confusion reportedly arose after one of the high school teachers received a phone call suggesting there was an "active shooter drill". As there was no scheduled drill, Morgan Nugent, principal of Osan American High School, said the institution went for a full lockdown.

"He [the teacher] reported this to me immediately. There was no scheduled school shooter drill on base so we have decided to error on the side of safety and went into a full school lockdown.

"Once we are given an all clear we will go ahead and continue the school day as is with a chance for a debrief to our kids at the end of the school day. Ultimately though your children are safe and we will continue to keep them safe."