No South Korean casualties have been reported in a powerful earthquake that struck off northern Japan on Saturday, the foreign ministry said.

The 6.9 magnitude quake occurred shortly after 6 p.m. off the coast of Miyagi prefecture, according to news reports. Its strength was revised downward from a magnitude of 7.2.

"As of now we understand that there have been no casualties among our nationals," a ministry official said.

"The ministry and the consulate general in Sendai immediately launched a response team after the quake and have continued to monitor the extent of damage in close communication with the Korean community," the official said, adding that consular assistance will be provided as needed. (Yonhap)