Japan endures about 20 percent of the world's major earthquakes and lives in constant fear of the "Big One." The archipelago has been hit by three moderate tremors in the past two days.

More than one million people including police, firefighters, troops and local volunteers on Friday practiced their response to a major earthquake registering 7.3 on the Richter scale.

Prime Minister Junichiro Koizumi, sporting a blue-gray workman's tunic, held a mock press conference.

"Due to the quake which occurred at 7:15 am, we've received reports that already many people were injured or died," Koizumi said.

"The government has set up an emergency counterdisaster center and ministers are now dealing with the initial response," he said.

Koizumi linked by a teleconference with Tokyo Governor Shintaro Ishihara and Bank of Japan Toshihiko Fukui on ways to rescue people and keep running the capital of the world's second largest economy.

A study by the Tokyo Metropolitan Government in March said a 7.3-magnitude earthquake would kill 5,600 people and damage 440,000 buildings, despite Japan's requirements that all construction be resistant to tremors.

The US military took part in the nationwide drills for the first time, with helicopters from Yokota air base in Tokyo ferrying people and relief materials.

The Seoul fire department also sent a delegation which worked jointly with its Tokyo counterparts to rescue people from fallen buildings.

Tokyo was jolted Thursday by a 4.8-magnitude quake, which was followed an hour later by a moderate tremor in the Russian-ruled Kuril islands off northern Japan.

On Friday, a quake registering 5.7 on the Richter scale struck Japan's southern Okinawa island chain. None of the quakes caused injuries or damage.

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