(CNN) -- The water three men were exposed to while working at the Fukushima Daiichi nuclear power plant had 10,000 times the amount of radiation typical for that locale, an official with the Japan nuclear and industrial safety agency said Friday.
The contamination is likely from the No. 3 reactor's core, the official, Hidehiko Nishiyama said.
He said there's a possibility of "some sort of leakage" -- including potentially from a crack in the unit's containment vessel.
The incident raised questions about radiation control measures at the plant as 536 people -- including government authorities and firefighters continued working there Friday, according to an official with the plant's owner, Tokyo Electric Power Co.
Workers are undertaking various measures to prevent the further release of radioactive substances into the air and beyond.