SEOUL, South Korea (AP) — A South Korean navy plane carrying four people crashed during a training flight on Thursday and it was not immediately known if there were casualties, the navy said.

The patrol plane left its base in the southeastern city of Pohang at 1:43 p.m. but fell to the ground due to unknown reasons, the navy said in a statement.

The navy is working to determine the status of the four people aboard the plane and why it crashed, the statement said.

An emergency office in Pohang said that rescue workers and fire trucks were dispatched to the site after receiving reports from local residents that an unidentified flying object fell and there was an explosion.

Pohang’s Nambu police station said the crash involved a navy patrol aircraft but it couldn’t immediately confirm whether there were any deaths or injuries.