The popular first-person shooter "S.T.A.L.K.E.R. 2: Heart of Chornobyl" is set in a fictional version of the restricted surroundings of the nuclear plant, which suffered a catastrophic meltdown in 1986.

"It was found that a considerable number of adventurer trespassers who illegally tried to enter the restricted area in search of extreme thrills were video game enthusiasts," Ukraine's border service said Thursday.

The warning came a day after the release of "S.T.A.L.K.E.R. 2", a long-awaited sequel to the game developed by Ukrainian studio GSC.

The survival game sees players, or "stalkers", navigate a post-apocalyptic exclusion zone around the plant filled with mutants and humanoid monsters.

The release proved so popular that the rush to download it triggered a "temporary decrease in internet speeds" across Ukraine, the digital transformation ministry said, with total data use up by "at least 35 percent" compared to a normal day.

The border service warned that the Chernobyl exclusion zone "is a restricted area closed to the public and subject to intense radioactive contamination. Illegal entry into and stay in this area is subject to both administrative and criminal liability."

Over 100 people from several countries including the United States, Germany and South Korea were detained for illegally entering the zone in 2021, before Russia's invasion, the border service said.

The number of trespassing incidents dropped when Ukraine introduced martial law in response to the invasion by Russia in 2022, but "they still happen", a source in Ukraine's border service told AFP.

"They are mostly Ukrainians who wanted to visit the Chernobyl zone and walk in places where you are not allowed to walk," the source added.

The Chernobyl exclusion zone is one of the most radioactively contaminated places on Earth, spanning a 30-kilometre (19-mile) radius around the plant.

Visits to the site were possible with a tour guide before the war but since Russia's invasion in 2022 the area has been completely closed off to tourists.