The quake was strong enough to sway buildings in Tokyo as it struck 200 kilometres (125 miles) to the northwest in Niigata prefecture near Hirokami village at 10:40 (0140 GMT).

Television footage showed people staying in shelters hurriedly lying down on the floor as the new tremor rumbled 10 kilometres (six miles) underground.

A building with a photo studio collapsed in the latest tremor in Ojiya city but two people inside were rescued alive, a local police official said, adding it was not known whether they were injured.

Weather officials said there was no danger of tsunami tidal waves.

The Niigata region was hit by Japan's worst earthquake in nearly a decade on Saturday.

The death toll from the initial tremor and subsequent powerful shocks stood at 31, with nearly 2,530 people injured and three others missing, police said.

About 103,000 people were staying at hundreds of shelters after leaving their homes for safety.

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