A powerful earthquake struck Japan’s Kumamoto prefecture on the southwestern island of Kyushu on Tuesday, killing at least 13 people and causing widespread destruction.

Rescue crews continued searching for survivors as authorities warned that strong aftershocks could continue over the coming days.

Here is what we know so far:

What happened in Japan?

The magnitude 7.1 earthquake struck the Kumamoto prefecture on Kyushu island at 4:30pm (07:30 GMT) on Tuesday, although the US Geological Survey (USGS) later revised its estimate to 6.8.

A tsunami advisory was issued immediately after the earthquake but was later lifted.

The earthquake caused widespread damage as buildings collapsed.

It sparked fires in Kumamoto City, the prefectural capital, trapped shoppers inside a partially collapsed shopping mall, cut power to thousands of homes, and left roads badly damaged.

Just after midnight on Wednesday (15:15 GMT Tuesday), a magnitude 4.1 aftershock struck Kumamoto prefecture, public broadcaster NHK reported.

Where did the earthquake hit?

According to the USGS, the epicentre was near the coastal city of Uto, about 48km (30 miles) southwest of Kumamoto City.

Kumamoto is located on Japan’s southwestern island of Kyushu, one of the country’s four main islands, about 90km (55 miles) east of Nagasaki.

As of 2019, Kumamoto City has an estimated population of 700,000.

The Kyushu region is also home to the Sendai Nuclear Power Plant in neighbouring Kagoshima prefecture, south of Kumamoto.

Officials said no abnormalities were detected at the two-reactor facility following the earthquake.

How powerful was the earthquake?

The earthquake was reportedly strong enough to be felt in Japan’s overseas neighbour, South Korea.

Its force caused significant infrastructure damage across Kumamoto. NHK footage showed parts of the Kyushu Expressway split apart, and a section of the wall surrounding Kumamoto Castle collapsed.

Authorities are still assessing the damage to buildings, bridges and other infrastructure.

What damage did the earthquake cause?

At the Aeon shopping mall in Kumamoto City, part of the second floor collapsed before a powerful explosion tore through the complex.

Employees helped evacuate about 200 shoppers when the quake struck, but the explosion came about an hour later, blowing out walls and exposing much of the steel framework.

NHK reported that 20 to 30 employees were initially unaccounted for. Witnesses also reported smelling gas in the area, although the cause of the explosion remains unclear.

The mall had reopened only last month after being rebuilt following the devastating Kumamoto earthquake in 2016.

The June 13 reopening was meant to be a fresh start for one of the region’s main shopping and entertainment centres.

After the 2016 disaster, a supermarket in the mall offered discounted rice balls to survivors, becoming a symbol of the recovery effort.

What do we know about the victims?

Japanese Prime Minister Sanae Takaichi said the death toll from the earthquake has risen to 13.

“Even now, there are people waiting to be rescued, and this is a race against time,” Takaichi told reporters in Tokyo on Wednesday.

Local media reported that two women in their 20s were found dead early on Wednesday inside the partially collapsed shopping mall.

Hospitals have treated dozens of injured people. One hospital received more than 50 patients, while another treated about 40 people, including 10 in a serious condition, according to public broadcaster NHK.

Around 260,000 people have been instructed to go to evacuation centres, Reuters reported.

Takaichi also urged residents and rescue workers to take precautions against heatstroke.

What’s the latest on the ground?

The Japan Meteorological Agency warns that strong aftershocks are possible for a week, with the highest risk in the next two to three days. It also warned of an increased risk of landslides in the hardest-hit areas.

More than 36,000 homes remain without electricity, while officials have raised concerns about heat-related illnesses as temperatures are expected to reach about 34C (93F) on Wednesday.

A hospital in Uki City, near the earthquake’s epicentre, said it was unable to operate after losing power in the quake.

The earthquake has also disrupted manufacturing across the region. Toyota said it would halt operations at three plants in southern Japan through Friday as it assessed the impact on suppliers and logistics.

Honda Motor also said it would extend the shutdown of its motorcycle plant in Kumamoto until Friday to allow repairs to parts of the factory damaged by the earthquake.

Why is Japan prone to earthquakes?

Japan sits on the Pacific Ring of Fire, where several major tectonic plates meet.

The country experiences thousands of earthquakes every year, as the Pacific, Philippine Sea, Eurasian and North American plates constantly shift against one another.

Strict building codes and regular earthquake drills have helped reduce casualties, but powerful earthquakes can still cause widespread destruction.

Minor tremors also occur, on average, every five minutes, according to Reuters.