The fire has spread to about 100 hectares (250 acres) of forest, Firsov wrote.
A forest fire was reported in the evacuated area surrounding the Chernobyl nuclear power plant late last week and it has increased radiation levels manifold.
Radioactive radiation, still present following the 1986 nuclear accident, made fighting the blaze considerably harder.
Radiation levels have soared to approximately 16 times higher than normal, according to Geiger counter readings posted on Facebook by Yegor Firsov, head of Ukraine's state ecological inspection service. But the emergencies service said radiation levels in the capital of Kyiv, about 100 kilometers south, were within norms. Fires in the zone are a regular occurrence.
On Sunday morning, the fire was not visibly burning and no increase in radiation in the air had been detected, the emergencies service said in a statement.
The Geiger counter reading usually shows 0.14 microsieverts per hour (μSv/h), but readings in the area on Saturday displayed 2.3 μSv/h, he said. A helicopter and three fire-fighting aircrafts were also deployed. Some of them start when residents set dry grass on fire in the early spring - a widespread practice in Ukraine, Russia and some other ex-Soviet nations that often leads to devastating forest fires.
Firefighters in Ukraine said on Monday they were using aircraft to extinguish one of two blazes that broke out on Saturday in a sealed-off zone around the Chernobyl nuclear plant, the site of a major nuclear incident in 1986. "Every year we see the same picture - fields, reeds, forests burn in all regions".
Shortly after the disaster, authorities built a vast "sarcophagus" around the No. 4 reactor as a temporary measure to limit the spread of radiation into the environment.
The disaster forced tens of thousands of people to relocate from the exclusion zone, although a small number remain to this day after refusing to leave.