(Edits headline)

By Sergiy Chalyi

ZAPORIZHZHIA, Ukraine (Reuters) -Residents in the southeastern Ukrainian city of Zaporizhzhia appeared calm on Wednesday after Kyiv's latest warning that Russian forces could trigger a catastrophe at the nearby Moscow-held nuclear power plant.

Both Russia and Ukraine on Tuesday accused each other of plotting to stage an attack on the Zaporizhzhia nuclear power plant, long the subject of mutual recriminations and suspicions.

Ukrainian President Volodymyr Zelenskiy said that Russian forces, who seized the plant shortly after their full-scale invasion in February 2022, had mined the roof of several reactors.

Experts from the U.N. nuclear watchdog based at the plant, Europe's largest, said on Wednesday they had seen no indications of explosives but that more access is needed to be sure.

The U.N.'s International Atomic Energy Agency has repeatedly warned of potential catastrophe from nearby military clashes.

Ukraine's health ministry on Tuesday released guidelines in the event of an emergency and urged residents to pack emergency bags, containing supplies like face masks and food, wrapped in plastic.

"If authorities have officially announced a radiation emergency, stay indoors or get out as soon as possible," it said in a statement. "Stay tuned for further announcements and follow the instructions."

"I think those who have prepared themselves shouldn't be afraid," said Olena Havrylenko, a 55-year-old doctor in Zaporizhzhia, about 75 miles (120 km) north of the station.

She added that listening to trusted experts and following reliable news sources was critical.

Despite the grim messaging, there were few signs of panic in the city of around 700,000, where 39-year-old Anton Savchenko rested near a fountain wearing large sunglasses.

"Of course we're following (the situation) and hope that everything will be alright," he said. "Atomic energy is no joke. Everyone's seen it before."

Other local residents Reuters spoke to said they were prepared to evacuate if necessary, or that they didn't believe an accident would be serious.

On Tuesday, Renat Karchaa, an adviser to the head of Rosenergoatom, which operates Russia's nuclear network, said Ukraine was planning to drop ammunition laced with nuclear waste onto the plant.

Neither side has offered evidence for their claims.

(Writing by Dan Peleschuk; Editing by Alexandra Hudson)