SLAVUTYCH, Ukraine — People streamed into the central square of Slavutych in the early hours of Sunday, placing candles on a large radiation hazard symbol laid out on the ground as a midnight commemoration began for those killed in the Chernobyl disaster 40 years ago and the thousands who risked deadly radiation exposure to contain its aftermath.

Residents show up for the vigil each year to commemorate the April 26, 1986, disaster. That day, Reactor No 4 at the Chernobyl Nuclear Power Plant in the former Soviet republic of Ukraine exploded, releasing more than 8 tons of highly radioactive material.

Over 60,000 square kilometers of land were contaminated, and more than 3.2 million people were affected to varying degrees. It remains the most severe nuclear disaster in the history of civilian nuclear energy.

About 600,000 people, often referred to as Chernobyl's "liquidators", were sent in to fight the fire at the nuclear plant and clean up the worst of its contamination. Thirty workers died within months from either the explosion or acute radiation sickness.

The accident exposed millions in the region to dangerous levels of radiation and forced a wide-scale, permanent evacuation of hundreds of towns and villages in Ukraine and Belarus.

The city of Slavutych, around 50 kilometers from the former plant, dates to this period. While most evacuees were resettled across nearby districts in the Kyiv region, in late 1986, authorities began building what would become the city to house workers from the Chernobyl Nuclear Power Plant and their families. The first residents moved in around 1988.

People of all ages gathered in the square, some arriving as families carrying spring tulips and daffodils.

Liudmyla Liubyva, 71, came to the ceremony with a friend. She used to attend with her husband, who worked at the Chernobyl Nuclear Power Plant but later developed a disability linked to radiation exposure, and lost the ability to walk, she said.

Liubyva said it was important to honor those who sacrificed their health in the aftermath of the disaster. "We all — young and old alike — must protect our land, because it is so vulnerable."

Soft music played in the background as poetry about the disaster drifted over loudspeakers. "Years pass, generations change, but the pain of Chernobyl does not fade," a woman's voice recited.

As the words echoed across the square, people dressed in white protective suits and face masks, symbolizing the liquidators, stood in silence holding candles.

Larysa Panova, 67, often recalls the day of the accident that forced her to leave her native hometown of Chernobyl, which is transliterated as Chornobyl, and begin a new life in Slavutych.

Though the new city has long since become home, she still thinks of the forests and rich nature of the place she left behind.

AGENCIES-XINHUA