The exercise came a month before Japan introduces an early quake warning system nationwide.

The central government held a drill at the prime minister's office, assuming the meteorological agency warns that a massive quake will strike within days.

"I issue a warning about a quake disaster. This quake is predicted to trigger very strong tremors and massive tsunami waves in wide areas," Abe, clad in a blue work uniform, said after a mock cabinet meeting.

"Tremendous damage is expected... Please be alert, follow instructions from relevant offices and act calmly," he said in an address to the nation.

Japan, which endures about 20 percent of the world's strong earthquakes, still has vivid memories of a 6.8 Richter-scale tremor on July 16 that killed 11 people in the Niigata central region.

The nation holds annual drills to commemorate the deadly September 1, 1923 Great Kanto Earthquake, which left more than 140,000 people dead or unaccounted for in and around Tokyo, and prepare for the next big one.

The most frequently forecast scenario is one which could devastate the Tokai region from around Mount Fuji in the east to Mie prefecture in the west -- including the city which top carmaker Toyota Motors is based in.

The July 16 Niigata quake also shut down a sprawling nuclear power plant, causing more than 60 problems including fires and a small amount of radiation leakage.

Taking into account possible damage to nuclear facilities, the head of the government's nuclear safety agency joined the day's emergency government meeting for the first time this year.

Local governments also held drills on separate disaster scenarios.

The Tokyo metropolitan government held a drill in cooperation with US forces, assuming a 7.3-magnitude quake hit the capital.

An amphibious ship of the US military was deployed to help people go home after the quake's hypothetical devastation.

Central Japan's Shizuoka prefecture, predicted to suffer most in the Tokai quake, held drills involving 270,000 people.

Shizuoka Governor Yoshinobu Ishikawa had a video conference with Abe, who was at his office in Tokyo and briefed by the local governor on quake damage.

Television footage from across the nation showed scores of citizens relaying buckets containing water in efforts to put out fire and fire fighters chain-sawing collapsed makeshift houses to rescue quake survivors.

An estimated 627,000 people took part in exercises across Japan on Saturday, according to Jiji Press news agency.

Japan will start sending earthquake warnings to the public on October 1, giving them vital seconds to prepare before one of the country's frequent tremors strikes.

The system made its debut earlier this year but so far has been confined to major businesses and public utilities. From October, the alerts will also be sent out via radio, television or public loudspeakers, which are commonplace in Japan.

The system can predict earthquakes seconds before they strike, prompting companies to develop a growing number of gadgets to alert people to an impending tremor.

The system works by detecting the first underground tremors -- the shear waves -- which come before more dangerous primary waves.

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