Wildfires in Ukraine have spread to just over a mile from the defunct Chernobyl nuclear power plant and a disposal site for radioactive waste, according to activists, as more than 300 firefighters work to contain the blaze.

A video posted by a Chernobyl tour operator showed flames and a cloud of smoke rising within sight of the protective shelter over the carcass of Chernobyl’s Unit 4 nuclear reactor, the site of the worst nuclear disaster in history.

If the fire engulfed Pripyat it would be an economic disaster, as supervised tourist visits provided valuable revenue.

Greenpeace said the fires were much bigger than the authorities realized.