A South Korean navy plane with four crew members crashed during a training flight on Thursday and it was not immediately known if they survived, the navy said.

The P-3C patrol plane took off from its base in the southeastern city of Pohang at 1:43 pm 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. There have been no reports of civilian casualties on the ground, it said.

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

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 aircraft fell onto a hill near an apartment complex and caused a fire.