Sirens ring out in the South Korean capital as Seoul hold a civil defence drill.

As part of a joint military exercise with the United States, areas of the capital came to a standstill as people practised what to do in an emergency.

Traffic stopped as people moved into safe places, such as train stations.

Underground in one subway, civilians and government officials learned CPR.

SOUNDBITE: JANG SUNG-GU, ACTION OFFICER OF CIVIL DEFENCE DIVISION AT SEOUL METROPOLITAN GOVERNMENT, SAYING (Korean):

"This exercise is a field for learning and exercising measures to deal with emergencies. This will teach our citizens how to escape safely or rescue injured people in time of emergency."

The annual exercise mobilizes thousands of U.S. and South Korean troops, focusing on defending South Korea in an emergency.

It comes amid tension between South Korea and its reclusive neighbour in the North.

North Korea has strongly denounced the drill, saying it preludes to war.