"There are no more open flames," but fires are still smouldering out of sight, said the deputy head of the emergencies ministry, Mykola Chechetkin, cited by Interfax- Ukraine news agency.
"Until it is completely extinguished, we will carry out measures to observe and douse it. I think we will carry out these measures for another 48 hours," he said.
A Ukrainian scientist meanwhile criticised the authorities for a lack of safety equipment for the firefighters including face-masks.
The blaze came within about 20 kilometres of Chernobyl after breaking out Tuesday afternoon, but officials said it posed no danger to the plant and radiation levels in the zone remained unchanged.
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The fire has now been reduced to about 70 hectares, down from the 320 hectares across which it had spread near the plant, which is about 100 kilometres from the Ukrainian capital Kiev, emergency services said today.
The area around Chernobyl was evacuated after the 1986 blast and the last reactor there was shut down in 2000 but some personnel still operate in the exclusion zone, where work is underway to build a new seal over the reactor site.
Officials gave few details of the possible cause of the fire but Ukraine's Interior Minister Arsen Avakov said authorities had not ruled out arson.
The fire struck just two days after Ukrainians marked 29 years since the Chernobyl nuclear disaster.