A GAS explosion and ensuing fire has ripped through a Russian "bio-weapons" laboratory where the world's most infectious viruses are stored.

The State Research Centre of Virology and Biotechnology has said a cylinder exploded in a lab, which is one of two places in the world to stockpile smallpox.

4 The State Research Centre of Virology and Biotechnology, known as Vector Credit: Prospekt/The Siberian Times

4 A major emergency was declared because of what is stored in the facility Credit: Rospotrebnadzor/The Siberian Times

4

The blast follows a series of explosions in top-secret weapons bases in the past few months.

Other highly lethal diseases that are stored there include Bubonic Plague, Anthrax and Ebola.

Located in Koltsovo, in the Novosibirsk region of Siberia, the site called the Vector Institute is thought to be where biological weapons were developed.

Some 13 fire engines and 38 firefighters entered the six-story building minutes as it was realised what the possible implications could be.

4 In the 20th century smallpox was responsible for between 300-400 million people being killed Credit: Getty Images

Russian media have reported that the “the situation was quickly upgraded from an ordinary emergency to a major incident”.

Following the blast, one worker was left with third degree burns. Further details are unclear.

The risk to the public from biological contamination has been downplayed.

Russian state media reported the facility’s head “emphasising the incident does not pose any biological or any other threat to the population”.

The fire was caused by the explosion of a gas canister but "no work with biological materials was going on there", a statement from the lab said.

MAJOR INCIDENT

The incident follows numerous blasts in nuclear and conventional weapons bases in the past few months.

On August 8 a deadly explosion at ballistic nuclear missile testing range near Nyonoksa, north-western Russia caused a spike in radiation levels and sparked the evacuation of a nearby village.

Officials claimed that no radiation had been released, although the city administration in Severodvinsk reported a rise in radiation levels – a contradiction that recalled Soviet-era cover-ups of disasters like Chernobyl.

On August 5, huge explosions and mushrooms clouds were witnessed nearby a weapons base in Kamenka, Siberian region of Krasnoyarsk

On July 1 a "blast" aboard a Russian nuclear "spy" submarine killed 14 crew members.

What is smallpox? During the 20th century it was responsible for 300-400 million deaths and in 1967 the World Health Organisation (WHO) estimated that around 15 million people had the disease and two million died in that year. Fortunately after various vaccination campaigns during the 19th and 20th centuries, smallpox was considered to be globally eradicated in 1979 by the WHO. But, now scientists are concerned the disease may be making a comeback because climate change is rapidly thawing the permafrost where the infected bodies are buried. During the 1890s, a major epidemic of smallpox broke out in a small Siberian town near the Kolyma River in Russia. The disease killed up to 40 per cent of the population and the bodies were buried in soil near the river, but now the water is thawing the banks three times faster than usual and the infected bodies are becoming exposed. The last person to die from smallpox was a woman named Janet Parker. The 40-year-old medical photographer from Birmingham died on September 11, 1978 - exactly one month after she started feeling unwell. Within days, she developed unsightly red spots on her back, limbs and face, but when a doctor was called, she was told she had chickenpox.

The plant is one of two places in the world, where the smallpox disease is stored.

The other place is at a high-security laboratory which is called the US centre for Disease Control in Atlanta.

Huge mushroom cloud rises above munitions depot in Siberia, Russia, after a series of massive explosions

MOST READ IN NEWS CREEPY CRAWLERS Dozens of horrifying 3ft-long robber crabs invade family's campsite BBQ GANGSTER NO 1 New 'El Chapo' seizes control of Mexico gang that sets rivals' heads on fire OUT OF THIS WORLD Man transforms into 'alien' after having nose REMOVED & splitting tongue FIT AND FIFTY 'World’s hottest gran' celebrates 50th as fans praise her youthful looks LASHED TO BITS Paedo collapses as he’s caned 52 times after being sentenced to 169 lashes SNAKES ALIVE Snake farm owner ‘pretended to adopt puppies before FEEDING THEM to serpents

Fifteen years ago, a scientist at Vector died after accidentally jabbing themselves with an Ebola-laced needle, leading to concerns about the safety standards.

The facility was set up in 1974 as a closed institute researching vaccines and "defences against bacteriological and biological weapons", Russian Interfax news agency reports.

Suspected Ebola case in Sweden as patient quarantined after vomiting blood

We pay for your stories! Do you have a story for The Sun Online news team? Email us at tips@the-sun.co.uk or call 0207 782 4368. You can WhatsApp us on 07810 791 502. We pay for videos too. Click here to upload yours.