Sunday, April 26, marks the 40th anniversary of the world’s worst nuclear power plant accident at the Chernobyl nuclear power station in the Soviet Union.

On April 26, 1986, the Chernobyl nuclear reactor melted down, but the rest of the world wouldn't learn how close it came to nuclear Armageddon until weeks later.

In the early hours of 26 April 1986, Reactor 4 at the Chernobyl Nuclear Power Plant exploded after a planned safety test went catastrophically wrong. The Chernobyl disaster was the result of a chain of critical errors — and its fallout was unprecedented.

On April 26, 1986, a fire and explosion at the Soviet Union's Chernobyl nuclear reactor north of Kiev, Ukraine, resulted in the world's worst civilian nuclear disaster.

Efrem Lukatsky, a Kyiv-based photographer for The Associated Press, was living in the city on April 26, 1986, when the explosion and fire struck the Chernobyl nuclear power plant, about a two-hour drive away.

In the weeks after the April 26, 1986, explosion and fire at the Chernobyl nuclear power plant, it was difficult to get any information about the scope of the disaster, aside from terse announcements from the government of the Soviet Union.

The BBC's Jessica Parker visits Pripyat, which was abandoned in 1986 after an explosion at the nearby Chernobyl nuclear power plant.

Following the April 26, 1986, explosion and fire at the Chernobyl nuclear power plant, soldiers, firefighters, engineers, miners and medics were summoned from across the USSR. They were known as “liquidators” — an ominous Soviet-era catchall term for those assigned to eliminate a problem.