Japanese officials have released a confronting video of what might happen in an eruption of Mount Fuji – depicting what looks like a nuclear explosion, followed by darkness and an icy winter.

Part of the five-minute film released this week shows a frightened woman covering her face with her hands as she watches a grey mushroom-shaped cloud rising above the mountain on a screen in Tokyo’s Shibuya district.

Fuji is Japan’s tallest peak at 3776 metres and is less than 100 kilometres west of Tokyo. It used to erupt about every 30 years, but has been dormant since 1707.

Local officials released the released computer- and AI-generated videos showing a simulation of what might happen to mark Volcanic Disaster Preparedness Day.

The footage is meant to prepare the 37 million residents in the greater Tokyo metropolitan area for potential disasters if the active volcano does blow.

“The moment may arrive without any warning,” it warns.

“Since we do not know when Mount Fuji will erupt and blanket us with volcanic ash, to protect ourselves and our loved ones we need to arm ourselves with facts.”

The dramatic footage shows clouds of smoke and ash erupting from Fuji’s summit, spewing boulders skyward and sending rivers of lava down its slopes.

The video shows lava steaming down the mountain’s side.

Within two days of the simulated eruption, Tokyo is blanketed in ash, with trains derailed and roofs collapsing.

It comes after an expert Japanese panel warned in March that a full-scale eruption of Fuji could generate 490 million cubic metres of ash — or 10 times the amount of debris created by the devastating 2011 Tohoku earthquake and tsunami.

Sharp particles of ash can not only bring darker skies, but might also harm people’s eyes and lungs and scratch glass.

“Volcanic ash is made up of fine, jagged particles,” the video warns.

“Its unique qualities pose many hazards to health and society.”

The panel warned ash from such an explosion could reach Tokyo in just over an hour.

The video also shows a family’s pantry stocked with canned food and a first-aid kit.

“We need to arm ourselves with facts and prepare for disaster in our daily lives,” it finishes.

The video depicts chaos in Tokyo soon after the “eruption”.

Tokyo’s government said there were no signs of an imminent eruption of Fuji.

“The simulation is designed to equip residents with accurate knowledge and preparedness measures they can take in case of an emergency,” it said.

The footage was criticised by some Tokyo residents.

“Are there actually any signs of eruption?” said 57-year-old hospital employee Shinichiro Kariya.

“Why are we now hearing things like ‘10 centimetres of ash could fall’, even in Tokyo? I’m wondering why this is happening all of a sudden.”

Another person said: “The thought of volcanic ash causing transportation chaos in the Tokyo metropolitan area is terrifying.”

But University of Tokyo professor and risk communication expert Naoya Sekiya said the local government regularly modelled scenarios for volcanic eruptions and earthquakes. That did not mean Fuji was about to erupt.

“There’s no particular significance to the timing,” Sekiya said.

Japan is highly vulnerable to natural disasters and is known for its planning for earthquakes, typhoons, floods, mudslides and volcanic eruptions.

It sits on the Pacific Ring of Fire and is home to 111 of the world’s roughly 1500 active volcanoes.

A month ago, Japan’s northern island of Hokkaido was hit by tsunami waves after a powerful 8.8-magnitude earthquake in the Kuril islands in Russia’s far east.

-with agencies