Survivors and victims' relatives of the Chernobyl tragedy observed a midnight vigil to mark the 26th anniversary of the worst civil nuclear tragedy in the history of mankind on Thursday.

Reactor #4 of the Chernobyl nuclear plant exploded at 1:23 am (GMT) on April 26, 1986, killing two people at the site. Dozens more died in the following months, forcing thousands to flee their homes.

The explosion was caused by a huge surge in power; an umbrella cloud rose skyward, spreading radioactive materials in the atmosphere in the explosion's aftermath.

The ensuing fire continued for 10 days, and nearly 4,000 tons of lead and sandbags were dropped on the site to cool the reactor. Ill-equipped firefighters also suffered radiation poisoning, causing many of them to eventually die or live with cancer for the rest of their lives.

Investigations into the causes for the disaster pointed to procedural and design errors.

Initially, Ukrainian authorities tried to keep the tragedy secret, which slowed the evacuation process in nearby villages.

It took nearly 30 hours to start the evacuation process in Pripyat, one of the affected villages, just three kilometers away from Chernobyl.

There are conflicting reports about the death toll. A Greenpeace report in 2006 put the number of fatal cancer cases at about 100,000, and health issues related to cancer cases reached over a quarter of a million.

According to an estimate by the International Agency for Research on Cancer (IARC), the Chernobyl tragedy will have caused 16,000 cancer deaths in Europe through 2065.

"By 2065 (i.e. in the eighty years following the accident), predictions based on these models [risk prediction models] indicate that about 16,000 cases of thyroid cancer and 25,000 cases of other cancers may be expected due to radiation from the accident, and that about 16,000 deaths from these cancers may occur," the IARC stated.

Every year, people who were evacuated from the surrounding villages following the nuclear accident gather at cemeteries to remember those who lost their lives in the tragedy.