POWER PLANT MELTDOWN
An alarm bellowed out at the nuclear plant on April 26, 1986, as workers looked on in horror at the control panels signalling a major meltdown in the number four reactor.
The safety switches had been switched off in the early hours to test the turbine but the reactor overheated and generated a blast the equivalent of 500 nuclear bombs.
The reactor's roof was blown off and a plume of radioactive material was blasted into the atmosphere.
As air was sucked into the shattered reactor, it ignited flammable carbon monoxide gas causing a fire which burned for nine days.
The catastrophe released at least 100 times more radiation than the atom bombs dropped on Nagasaki and Hiroshima.
EVACUATION
Soviet authorities waited 24 hours before evacuating the nearby town of Pripyat - giving the 50,000 residents just three hours to leave their homes.
After the accident traces of radioactive deposits were found in Belarus where poisonous rain damaged plants and caused animal mutations.
But the devastating impact was also felt in Scandinavia, Switzerland, Greece, Italy, France and the UK.
An 18-mile radius known as the “Exclusion Zone” was set up around the reactor following the disaster.
DEATH TOLL
At least 31 people died in the accident - including two who were killed at the scene and more who passed away a few months later from Acute Radiation Syndrome.
The actual death toll is hard to predict as mortality rates have been hidden by propaganda and reports were lost when the Soviet Union broke up.
In 2005, the World Health Organisation revealed a total of 4,000 people could eventually die of radiation exposure.
About 4,000 cases of thyroid cancer have been seen since the disaster - mainly in people who were children or teenagers at the time.
MUTATIONS
Farmers noticed an increase in genetic abnormalities in farm animals immediately after the disaster.
This spiked again in 1990 when around 400 deformed animals were born - possibly as a result of radiation released from the sarcophagus intended to isolate the nuclear core.
Some animals were born with extra limbs, abnormal colouring and a smaller size.
Animals that remained in the exclusion zone became radioactive - including as many as 400 wolves, which is the highest density wolf population on the entire planet.
The Eurasian lynx - once believed to have disappeared from Europe - thrived in Chernobyl as there were no humans to run them out.
Birds were also affected by radiation, with barn swallows having deformed beaks, albinism and even smaller brains.
The radioactive animals all live in the "Red Forest", which got its name after the trees turned crimson in the fallout.
CHERNOBYL NOW
The site and Pripyat has been safe for tourists to visit since 2010.
There are around 160 villages in the Exclusion Zone.