A dozen South Korean fighter jets flew over major cities to simulate North Korean airstrikes. Trains ran at low speeds in a symbolic move to join with other stopped vehicles. In downtown Seoul, about 30 miles (50 kilometres) from the heavily militarized border and within easy range of North Korean artillery, the city’s congested streets momentarily cleared as traffic halted.

There was no penalty for not going to shelters, but authorities encouraged participation, sending out word through the media and posting notices in residential areas. Officials said about 11 million of South Korea’s 49 million people took part in the drill.

Lim Soo-ja, 68, was one of those who didn’t go to underground shelters, standing instead near Namdaemun market in central Seoul.

“I am too tired to move around, and I did not know where I should go,” she said.

At Seoul’s Ahyeon Middle School, 27 students sat in their classroom, dressed in winter coats and wearing white cotton masks. When the sirens rang, the students lined up in front of the classroom door before marching out to a subway station. Teachers shouted, “No running, no shouting and no talking,” but many students ignored them and ran to the station.

“We will need these evacuation plans and skills sooner or later in case war breaks out, and I think war can happen any time,” said Han Yoo-jin, 16.

In Paju, a city near the border with North Korea, dozens of residents ran to underground parking lots and donned gas masks in a drill against chemical, biological and radiological attacks. Rescue workers wearing gas masks and protective suits also brought residents pretending to be infected with chemical agents to ambulances.

The drills came amid stepped-up diplomatic moves by the United States and regional powers.

New Mexico Gov. Bill Richardson, on his way to visit North Korea, was scheduled to stop in Beijing on Thursday. Richardson has often acted as a diplomatic troubleshooter and has made regular visits to North Korea.

Also Wednesday, U.S. Deputy Secretary of State James Steinberg arrived in Beijing for talks with Chinese State Councilor Dai Bingguo, Beijing’s top foreign policy official. Dai returned last week from talks in Pyongyang with North Korean leader Kim Jong Il.

China has come under growing pressure from the United States and others to push ally North Korea to change its behaviour.

South Korea’s chief North Korea nuclear envoy travelled to Russia for meetings Wednesday with his Russian counterpart.