Homes, roads and railway lines were swept away when huge hillsides collapsed, as thousands of tonnes of mud was dislodged by the thunderous seismic tremors.
Buildings were reduced to rubble, including a university dormitory and apartment complexes, with dozens of people unaccounted for over a wide area.
“We are aware of multiple locations where people have been buried alive,” chief cabinet secretary Yoshihide Suga told a press conference.
“Police, fire-fighters and Self Defence Force personnel are doing all they can to rescue them.”
The quake came as emergency responders were working to reach areas already affected by a 6.2 magnitude tremor that struck late Thursday.
Adding to worries was the eruption of a nearby volcano, although seismologists cautioned there was no evidence of a link and said activity was limited.
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