MASHIKI, Japan (AP) — A powerful earthquake with a preliminary magnitude of 7.3 struck southern Japan early Saturday, barely 24 hours after a smaller quake hit the same region and killed nine people.

While it was not immediately clear whether the latest quake increased the death toll, authorities said hundreds of calls had come in from residents reporting people trapped inside houses and buildings. The Fire and Disaster Management Agency said 66 people were trapped inside a nursing home in Mashiki, the hardest-hit town, and rescue efforts were underway. No other details were immediately available.

More than 400 people were treated at hospitals, but most of their injuries were not life-threatening, the Japanese broadcaster NHK said, citing its own tally. Video showed a resident, apparently rescued from underneath a collapsed house, on a stretcher being taken to a hospital by ambulance.

The quake shook the Kumamoto region at 1:25 a.m. Saturday, and several aftershocks soon followed. Japan’s Meteorological Agency issued an advisory for a tsunami up to 1 meter (3 feet) high along the coast west of the epicenter in Kumamoto, but it was lifted less than an hour later.

The agency upgraded the magnitude to 7.3 from an initial reading of 7.1. Compared to the temblor that struck late Thursday night just south of the town of Mashiki, the most recent quake and aftershocks appeared to be moving east, spreading damage to the northeast.

Chief Cabinet Secretary Yoshihide Suga, in an emergency news conference early Saturday, said more than 300 calls came in to the Kumamoto police and another 100 to police in nearby Oita, seeking help and reporting people trapped or buried underneath debris.

Prime Minister Shinzo Abe, looking tired, said damage from the magnitude 7.3 quake could be “extensive” and urged rescue workers to do their utmost to help those trapped in the rubble.

Sirens of patrol vehicles could be heard in the background as NHK reported from Mashiki. The asphalt outside the town hall had a new crack, apparently made by the latest earthquake. In nearby Uto City, police reported that the City Hall building appeared to be unsafe because of damage.

The Nuclear Regulation Authority said no abnormalities were found at the Sendai nuclear plant, where the only two of Japan’s 43 reactors are online. NHK video showed stones tumbled from the walls of historic Kumamoto Castle, and a wooden structure in the complex was smashed, adding to damage from Thursday’s quake.

At the Ark Hotel, east of the castle, hotel guests woke up to strong shaking and a warning siren. Hotel staff told guests, including tourists and journalists covering the quake, to evacuate their rooms and gather in the lobby for safety.

Thursday’s weaker magnitude 6.5 earthquake brought down buildings and injured about 800 people, in addition to the nine deaths. The epicenter of Saturday’s earthquake was about 12 kilometers (8 miles) northwest of Thursday’s and, at a depth of about 10 kilometers (6 miles), Saturday’s quake was shallower.

Since Saturday’s quake was bigger, Thursday’s was technically a foreshock, a Meteorological Agency official, Gen Aoki, told a news conference.

Saturday’s temblor hit residents who were still in shock from the previous night’s quake and had suffered through more than 100 aftershocks in the interim.

Yuichiro Yoshikado said Thursday’s quake stuck as he was taking a bath in his apartment in Mashiki.

“I grabbed onto the sides of the bathtub, but the water in the tub, it was about 70 percent filled with water, was going like this,” he said, waving his arms, “and all the water splashed out.”

“It’s as if all control was lost. I thought I was going to die and I couldn’t bear it any longer.”

A bright spot, broadcast repeatedly on television Friday, was the overnight rescue of an apparently uninjured baby, wrapped in a blanket and carried out of the rubble of a collapsed home.

Yoshikado, whose building was undamaged despite the intense shaking, checked the damage at his aunt and uncle’s home nearby. Kitchenware was scattered on the floor, and a clock had stopped around 9:26 p.m., the time of Thursday’s quake. Power and water had yet to be restored, and many in the neighborhood had not returned because of the aftershocks.

About 44,000 people stayed in shelters after Thursday’s quake.

The dead included five women and four men, the Fire and Disaster Management Agency said. One man was in his 20s, and the rest of the victims ranged from their 50s to one woman in her 90s. Eight of the nine victims were from Mashiki.

There were varying reports on the number of injured Thursday. Suga, the government’s chief spokesman, said at least 860 people had been injured, 53 seriously. Kumamoto prefecture tallied 784 injured.

Suga said 1,600 soldiers had joined the relief and rescue efforts. TV reports showed troops delivering blankets and adult diapers to those in shelters.

With water service cut off in some areas, residents were hauling water from local offices to their homes to flush toilets.

Suga said there were no abnormalities at nearby nuclear facilities. The epicenter was 120 kilometers (74 miles) northeast of Kyushu Electric Power Co’s Sendai nuclear plant, the only one operating in the country.

Most of Japan’s nuclear reactors remain offline following the meltdowns at the Tokyo Electric Power Co.’s Fukushima plant in 2011 after a magnitude 9.0 earthquake triggered a huge tsunami.

According to the Japan Meteorological Agency, Mashiki sits near two faults on Kyushu. The area is also near Mount Aso, a huge, active volcano. JMA officials said the quake was unusually strong for Kyushu.