A fresh 6.5 magnitude earthquake has struck southern Japan – causing fires to spread and dozens of houses to collapse, trapping people underneath.

The powerful tremor was reported 6.6 miles southwest of Kumamoto at 4.03pm UK time (12.03am local time) – two-and-a-half hours after a 6.2 magnitude quake hit the same area, according to the US Geological Survey.

Although no tsunami risk has been reported, about 100 people have been admitted to hospital, including 10 with serious injuries.

Local police reports suggest at least one person trapped under a house has died, while another was killed by fire.

A third person is “without vital signs”.

A large blaze has broken out in Mashiki, a town of about 34,000 people not far from the quake’s epicentre, and aerial footage has shown firefighters attempting to bring the flames under control.

Local media reports suggest 16,000 households in the area are without electricity, while 38,000 homes have lost their gas supply.

One of the earthquakes registered at the highest possible level of Japan’s seven-scale system for measuring seismic intensity – and a quake of that size usually means it is “impossible to move at will” as people are “thrown by the shaking”.

Scientists from Japan’s Meteorological Agency have warned “relatively strong” aftershocks are expected in the coming days which could cause landslides and more buildings to collapse, NHK has reported.

Meanwhile, the US Geological Survey has upgraded its damage assessment to red, which indicates extensive damage is probable and that the disaster is likely widespread.

The tremors derailed an out-of-service, high-speed bullet train as it was making its way back to a depot but no one was injured.

Nuclear regulators in Japan have said there are no reported problems at the only online power plant in the region.

Japan’s chief cabinet secretary Yoshihide Suga has said at least 19 homes have collapsed – and emergency services have received hundreds of phone calls to report damage to buildings.

He confirmed that 350 military personnel have been sent to help with the rescue effort, and added: “Because of the night darkness, the extent of damage is still unclear … I ask people in the disaster zone to act calmly and help each other.”

Many people had already left their homes when the latest earthquake struck, and photographs from the scene showed worried evacuees clinging on to their loved ones.

In March 2011, a 9.0 magnitude earthquake off the coast of northern Tokyo caused tsunami waves which killed nearly 20,000 people and caused a meltdown at the Fukushima nuclear power plant.