VINNYTSIA, Ukraine — Firefighters have struggled to control wildfires burning through radioactive forest in the abandoned territory around the Chernobyl nuclear plant, where radiation levels are considerably lower than they were immediately after the 1986 accident but still pose risks.

Radiation readings near the wildfires, where smoke is swirling about, have been elevated, with the wind blowing toward rural areas of Russia and Belarus for most of the past week. The wind shifted Friday toward Kyiv, the Ukrainian capital, but authorities say the radiation level is still normal in the city, whose population is about three million.

But Saturday’s strong winds could spread the fires to the remnants of the nuclear plant and the equipment that was used to clean up the disaster, said Kateryna Pavlova, the acting head of the agency that oversees the area, in a telephone interview. “At the moment, we cannot say the fire is contained,” Ms. Pavlova said.

After the 1986 Chernobyl disaster, authorities created an area around the plant known as the Zone of Alienation, a rough circle with a nearly 18-mile radius, fenced off with barbed wire. Access to the zone is limited to workers who manage the site and tourists who take guided excursions.