It started as a game. Perhaps bored on a calm summer day on Sakhalin Island, off the coast of Russia, a construction worker stopped to film his dog playfully standing off with a bear cub.

Laughing from the confines of a worker’s shed, colleagues joked over the interaction as the curious bear cub edged closer to them, scaring off their dog.

But the mood suddenly took a turn as a mother bear slowly appeared from behind a ledge with another cub in tow. 

The man was powerless to act as he held the camera on the emerging trio, stalking carefully up to the shed. And then, in a split second, they pounced. The camera abruptly cut out.

In harrowing footage, the man appeared to capture the moment a bear killed three construction workers and left two in critical condition in 2014.

The horrifying footage went viral, racking up millions of views around the world as a spate of similar attacks sparked fear around the country.

Footage from the attack began as colleagues took a moment of respite in a wooden shed in a thick forest on the Russian island.

The men seem fascinated by their dog playing with a bear cub, promptly chased back inside the hut.

The cub stops short of entering the building and backs off as the dog counters, tail wagging from side to side.

The exchange goes back and forth, the cub nervously backing off as the dog finds the courage to chase it away from the frame of the structure.

And then, in turn, the cub chases the dog back into the apparent safety of the wooden hut, narrowly missing it as it takes a swipe.

A man dressed in high-visibility clothing stands to get a better look as the bear falls back and waits for support.

From behind a slope, a second head anxiously appears, pressing carefully towards the building. 

Two cubs now look on at the men, separated only by the dog standing guard, ears pricked up to attention.

Lumbering up the hill, a much larger bear emerges, eyeing the men up before sniffing around, and sticking close to her cubs.

With her head pointed down and eyes trained on the little building, she makes a slow step forward before bursting into a charge.

The camera shakes suddenly and a flash of red is seen as the workers desperately try to escape.

According to contemporary reports, they were not so lucky.

Three workers reportedly died in the attack on Sahkalin Island, believed to have taken place in June 2014.

Two more were left in critical condition.

What happened to the dog was unclear, and the footage from the other man filming was could not be found.

Some disputed the authenticity of the video, according to the Mirror. The Guardian reported that the attack had been ‘partially filmed’, citing the clip. 

The attack came amid a spate of bear attacks on the island and wider Russia.

Three bears were reported to have been killed following what Russian media identified as a ‘surge of bear-related violence in eastern Russia’.

Two were shot on the island of Sakhalin in late June. One was reportedly begging for food on a local road, becoming aggressive when travellers tried to pet it.

The brazen animal, undeterred by attempts to scare it off, ‘continued to return with enviable persistence’ and had to be shot, regional Agriculture Ministry official Andrei Zdorikov told Interfax.

A second was shot for ‘behaving inadequately’ when it attacked and killed livestock and geese, and attacked a dog on the island.

Workers in Russia’s remote forests, often miles from civilisation, remain particularly exposed to bear attacks. 

Last year, video taken at a gas-drilling facility in Siberia captured the moment a brown bear entered the compound and savaged two gas workers.

Footage showed three dogs keeping a careful distance from the bear as it patrolled the camp.

A voice called out to the dogs to get away.

But it was too late. The bear made its way into the grounds of the facility and chased one of the dogs around a vehicle in the heavy snow.

As one man leaves a trailer, the bear emerges from behind some bags of chemicals and attacks.

One man was forced onto the snow by the animals as others tried to deter it with a fire extinguisher.

As the bear vanishes with the workers, one onlooker calls out: ‘Where is he?’

Another responds: ‘He’s ****** – [the bear] ate him there.’

The two men were in the smoking room of their plant when they saw a pack of dogs chasing something, say reports.

One of the pair – a mechanic – opened the door to chase away the bear but it immediately attacked him.

Footage captured the panic as the men tried to spray the animal with fire extinguishers and scare it off with flares and a gas spray.

Eventually the bear loosened its grip on the mechanic but immediately grabbed and savaged the plant’s foreman.

Workers called in a local hunter who came and shot the bear some 20 minutes after the attacks.

The two men were given first aid at the site and rushed by helicopter to hospital.

Bears are typically reserved and prefer to keep to themselves, avoiding contact with humans unless provoked, hungry or sick.

But like many animals, they do have a ‘critical space’ that they will defend if push comes to shove.

This is complicated by humans expanding into animals’ natural habitat, and threatens employees working on logging or energy extraction sites build in the remote wilderness.

In the Sakha Republic, in eastern Russia, in 2014 a bear broke down the door of a residential trailer and bit a woman inside, before it was scared away by her screaming.

Just days before, another bear on Iturup island ambushed a child as he was walking home from his grandmother’s house.

The boy was dragged to the shore and later required 170 stitches from horrifying injuries, saved only by the police arriving and shooting it.

Adult brown bears in Siberia and Russia’s far-east can weigh as much as 1,300lbs (590kg), and will become especially aggressive if needed to protect their cubs.