Japan's meteorological agency said the 7.0 magnitude quake hit off the country's southern coast, near to the island of Okinawa.

The tsunami warning was quickly downgraded to an advisory and there were no immediate reports of casualties.The quake occurred at a depth of 6.2 miles (10 kilometers) at 5:31am local time.

At first the agency predicted a tsunami up to 3 feet (1 metre) near the Okinawan coast but said later it had observed only a small swelling of tide.

Ryota Ueno, a town official in the Nishihara district of Okinawa, said: "I was fast asleep when the quake hit and I jumped out of bed. "It felt like the shaking lasted forever."

Japan is one of the world's most earthquake-prone countries. (Sky News)