An unexplained carpet of foamy bubbles filled streets in the centre of the southern Japanese city of Fukuoka in the early hours of Saturday morning – shortly after tremors from a devastating earthquake of magnitude 7.3 shook the town.

Twitter users posted pictures of the mysterious foam, with one calling it “disgusting”.

“I saw it just after the earthquake,” said Kazuki Nabeta, who lives in the busy central district of Tenjin, where the bubbles were found.

Some have speculated that the earthquake may have caused an underground pipe to burst.

Japan aftershock hits during Al Jazeera live report

“People were posting pictures on Twitter and it was near my house, so I went out to have a look,” said Mr Nabeta.

In pictures: Japan earthquakes Show all 20 1 /20 In pictures: Japan earthquakes In pictures: Japan earthquakes In pictures: Japan earthquakes Rescuers check the damage area caused by earthquakes in Minamiaso, Kumamoto prefecture AP In pictures: Japan earthquakes Policemen search for survivors at a landslide site after earthquakes in Minami-Aso, Kumamoto prefecture Getty Images In pictures: Japan earthquakes A search operation for missing persons is conducted around an area of mountain lodges which were buried in a landslide caused by earthquakes in Minamiaso, Kumamoto prefecture AP In pictures: Japan earthquakes Villagers gather in an evacuation center following a series of earthquakes in Minami Aso EPA In pictures: Japan earthquakes A scarred mountainside following a major landslide caused by a series of earthquakes in Minami Aso EPA In pictures: Japan earthquakes Japan Ground Self-Defense Force soldiers conduct search and rescue operations at an apartment which collapsed following an earthquake in Minamiaso town Reuters In pictures: Japan earthquakes A resident walks past collapsed houses in Mashiki AP In pictures: Japan earthquakes A landslide is seen after the earthquake in Minamiaso AP In pictures: Japan earthquakes Rescue workers from Japan's Ground Self-Defense Force dig a vehicle out from mud at a landslide site in Minamiaso EPA In pictures: Japan earthquakes Rescuers guide dogs to search for victims buried in a landslide due to the recent earthquakes in the village of Minami-Aso in Kumamoto prefecture Getty Images In pictures: Japan earthquakes A local resident rests with a pet dog at an evacuation center after an earthquake in Mashiki town Reuters In pictures: Japan earthquakes Collapsed houses caused by an earthquake are seen in Mashiki town Reuters In pictures: Japan earthquakes A shop clerk cleans broken wine bottles following an earthquake in Kumamoto city Getty Images In pictures: Japan earthquakes A woman cleans up in front of her collapsed house in the town of Mashiki, Kumamoto prefecture Getty Images In pictures: Japan earthquakes Resident Nobuyuki Morita (R) and his wife look around a room in their house in the town of Mashiki, Kumamoto prefecture Getty Images In pictures: Japan earthquakes Policemen search for missing people in a damaged neighbourhood following twin earthquakes in Mashiki Getty Images In pictures: Japan earthquakes Local residents evacuate from the town centre in Kumamoto Getty Images In pictures: Japan earthquakes Rescue team saved a man from his house buried alive Getty Images In pictures: Japan earthquakes An eight-month-old baby is carried away by rescue workers after being rescued from her collapsed home caused by an earthquake in Mashiki town Reuters

“There was a fire engine there. There wasn't anything special about it – it was normal foam.”

Fukuoka is 90km away from Kumamoto, where the strongest tremors were felt.

Residents of Fukuoka reported strong shaking but little damage from the two quakes, which took place on Friday and Saturday.

At least 29 people have been killed by the earthquakes, which injured more than 1,500 and left many more homeless.