The normal radiation monitoring system at Ukraine's Chernobyl plant has been taken offline due to a massive cyberattack, forcing employees to use hand-held counters to measure levels, officials said Tuesday.

The station's Windows systems was turned off "due to the cyberattack", said Ukraine's agency in charge of the exclusion zone around the plant. A spokesman told AFP employees now "go out and measure the (radiation) levels with hand-held meters."