Incinerated coronavirus bodies, nuclear fallout, and pollution were among theories to explain mysterious black rain falling on parts of Japan.

Soot-coloured rainwater was reported to authorities and on social media by people living in several wards in Saitama Prefecture in Japan, on 2 March.

The majority of 'black rain' reports came from the city of Hasuda - but other affected areas included Ageo, Iwatsuki and Kuki, also in Saitama.

Hasuda City officials issued a statement saying they were investigating the matter after receiving multiple complaints of 'black puddles in roads and on cars', according to SoraNews24.

Dark black blobs of rainwater collect on a window in Saitama Prefecture in Japan, creating an ominous picture for its citizens

Swirling soot-coloured puddles collect outside a person's property. Other similar sites were also reported collecting on and dripping from cars

Some Saitama citizens expressed concern over possible nuclear-related materials in the atmosphere, many on Twitter using #blackrain.

'Black rain came down today over a wide area,' said one person on Twitter.

'It looks like oil and is under investigation. They said they checked radiation levels and nothing unusual was found. Black rain is disturbing,' they added.

Another person wrote: 'That's a little too scary.' While another said: 'That's about as bad an omen as you can get these days.'

Hasuda City officials were said to have measured radiation levels and found 'nothing out of the ordinary'.

However, they added that the cause of the black rain water was a mystery and further investigation was necessary.

A person's balcony fills up with sooty rainwater, collecting in little black clumps like iron filings

More sooty water cascading from this hybrid car, creating dark streaks along the white body

Another Twitter user wrote: 'Are they secretly burning the bodies of coronavirus victims?'. While another said: 'Didn't North Korea fire missiles on that day?'

One person on social media speculated whether oil had fallen from a plane passing overhead.

Another, sounding slightly more panicked, wrote: 'This is fine. Everything's fine.'

People who witnessed the black rain covering their homes and property were understandably unnerved, as similar ominous signs were also reported during the Second World War.

The United States dropped the world's first deployed atomic bomb from a B-29 bomber over the Japanese city of Hiroshima on 6 August 1945.

Three days later the US dropped a second A-bomb over Nagasaki. An estimated 120,000 people were killed during both catastrophic blasts.

Radioactive material was sent up into the atmosphere at the time causing 'black rain' to fall over the areas of nuclear attack.

Scientists who tested a school uniform worn by a girl exposed to the rain contaminated by the Hiroshima bombing were able to detect Caesium-137, a radioactive isotope, 70 years later.

However, no nuclear activity was reported in Saitama and some said the likely explanation for the black rain was pollution, SoraNews24 said.

A collection of black bubbles on a silver vehicle vent, caught on camera by a Saitama citizen

It later emerged that a 'gigantic' fire had broken out in Hasuda around the time of the rainfall.

It was the blaze, at what is thought to be a large commercial building, that was speculated to be the cause of the black rain.

'It’s pretty easy to see how that much smoke could mix in with and dye much of the downwind precipitation black,' SoraNews24 said.

Other speculation about the fire's link to the black rain also appeared online.

'I don't know if this has anything to do with it, but there was a fire in the area that same day,' one person wrote.

'I think it was caused by a fire in the area,' said another.

'It was a fire at a plastic factory. There you go!' said a third.

One SoraNews24 reporter said: It doesn’t explain why Hasuda City never acknowledged this on their website.

'At a time when the dispersion of information is more important than ever, it’s very unsettling that they were either unaware of the gigantic fire in their own city, or didn’t feel it was necessary to mention while people online were speculating about mass-cremations and North Korean missiles,' they added.