A strange sea of bubbles filled streets in a southern Japanese city in the early hours of Saturday morning, after an earthquake and several aftershocks rattled the south of the country.

In the Tenjin area of Fukuoka city, motorists and pedestrians made their way through the foamy mess after it spilled out onto the streets.

Some reported that an underground pipe burst, releasing the material, but little information was immediately available.

SEE ALSO: Powerful earthquake rattles southern Japan

An earthquake rattled the area shortly before the foam appeared in the street, leading many to believe the weird white substance was linked to the quakes.

Residents of Tenjin shared images of the foamy stuff on Twitter, but most seemed baffled about what the substance could be.

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, Japanese broadcaster NHK said a number of calls were coming in from residents reporting people were trapped inside houses and buildings. 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; the advisory was lifted less than an hour later.

Sirens of patrol vehicles were heard in the background as NHK reported from the hardest-hit town of Mashiki. The asphalt outside the town hall had a new crack, apparently made by the latest earthquake.

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

At the Ark Hotel, east of the castle, hotel guests woke up to strong shaking and a warning siren. Hotel staff asked 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 killing nine. 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.

Additional information from the Associated Press.

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