The catastrophic Chernobyl nuclear accident in Ukraine, then part of the Soviet Union, marked its 33rd anniversary on Friday.

Axar.az reports citing foreign media.

On April 26, 1986, a sudden surge of power during a reactor systems test destroyed unit 4 of the nuclear power station at Chernobyl, some 110 kilometers (68.3 miles) from Ukraine’s capital, Kiev.

"#FBF (Flash Back Friday) to the Chernobyl nuclear disaster 33 years ago. The women, men and children affected by radioactive contamination must never be forgotten," the UN said on Twitter, designating April 26 the International Chernobyl Disaster Remembrance Day.

The UN said on its website that 31 people were killed in the immediate aftermath of the accident, while millions more were affected.

According to the official numbers, roughly 8.4 million people in the former Soviet territories of Belarus, Russia, and Ukraine got the largest exposure to radiation in the form of a cloud.

Later research into the accident showed that the radioactive clouds reached as far as the U.S. and China.

The UN also said that 155,000 square kilometers of these three countries were contaminated, equal to almost half of Italy, and over 400,000 people were displaced.

Fear of spreading radiation gripped many in Turkey’s Black Sea region, the area nearest Ukraine, but authorities reassured the public that there was no cause for concern.