There is another fire at the No. 4 reactor at the Fukushima No. 1 nuclear power plant, Tokyo Electric Power Co. said at dawn on Wednesday.
The worker at the plant saw the fire at 5:45 a.m. on the fourth floor of the reactor's building, according to report by Kyodo News. The plant operator said it had reported the incident to firefighters and local governments.
The location was the same place where there it was believed to be a hydrogen explosion which caused a fire Tuesday morning.
Earlier engineers had shown concern that two more reactors at the Fukushima Dai-ichi complex may have become unstable.
Plant operators were considering the removal of panels from units 5 and 6 reactor buildings to prevent a possible buildup of hydrogen, the International Atomic Energy Agency (IAEA) said in a statement.
It was a buildup of hydrogen at units 1, 2, and 3 that led to explosions at the Dai-ichi facilities in recent days.
Units 5 and 6 at the plant were reportedly filled will nuclear fuel but not in production when the huge quake and tsunami struck. Initially, they were regarded as stable, but last night nuclear officials in Japan warned temperatures were rising.
The power for cooling is not working well and the temperature is gradually rising, so it is necessary to control it, said Chief Cabinet Secretary Yukio Edano.