Ukraine is marking the 32nd anniversary of the Chernobyl nuclear disaster on April 26 with a memorial service and a series of events in remembrance of the world's worst-ever civilian nuclear accident.

In neighboring Belarus, an opposition-organized event will also be held to commemorate the disaster.

In Ukraine's capital, Kyiv, hundreds of people marched at midnight to the Memorial Hill of Chernobyl Heroes where they laid flowers and lit candles. At 1 a.m. on April 26, an Orthodox service and a prayer to commemorate Chernobyl victims were performed at the site.

President Petro Poroshenko, on April 26, wrote on Facebook that Chernobyl "will forever remain an open wound for us."

"Today, we have to do everything to prevent a repetition of that tragedy... the Chernobyl zone must now become a place of new technologies, a territory of changes,' Poroshenko wrote.

In Belarus, the opposition plans to hold a march in Minsk known as the "Chernobyl Path" later on April 26.

The march has been held in the Belarusian capital since 1988 to commemorate the disaster in neighboring Ukraine, which also contaminated large swaths of territory in Belarus.

An explosion on April 26, 1986, blew the roof off the building housing a nuclear reactor and spewed a cloud of radioactive material high into the air -- drifting across Ukraine's borders into Russia, Belarus, and across large parts of Europe.

About 30 people died in the immediate aftermath and thousands more are feared to have died in the years that followed from the effects of the disaster -- mainly exposure to radiation.

On April 25, the Vienna-based UN Scientific Committee on the Effects of Atomic Radiation said that around 20,000 thyroid cancer cases were registered between 1991 and 2015 in the area surrounding the reactor, which takes in all of Ukraine and Belarus, as well parts of Russia.

The UN scientists said that since the accident, 1-in-4 thyroid cancer cases have been caused by radiation in the region.

In November 2016, a huge arch was placed over the stricken reactor to prevent further leaks of radiation. The project -- funded by the European Bank for Reconstruction and Development -- cost $1.6 billion.

With reporting by RFE/RL's Belarus Service, 112 Ukrayina, and pravda.ua