An earthquake measuring 6.5 on the Richter scale struck northeastern Japan early on Monday, after which officials issued a tsunami alert, Japanese media reported.

Highly radioactive water detected at the reactor number two at the damaged Fukushima Daiichi nuclear power plant is a result of a partial meltdown of fuel rods, Japanese government spokesperson Yukio Edano said, underscoring that the government believes that melting of the fuel rods has ceased.

According to Edano, the Nuclear Safety Commission informed the government that they believe radioactive water that leaked from the reactor came into contact with fuel rods which partially melted at one point.

Contaminated, highly radioactive water was found at the basement of the reactor's turbine building, Kyodo news agency reported.

Removal of contaminated water from the Fukushima plant meanwhile continues, in an effort to enable engineers to restore plant’s cooling systems, and the government pointed out that it will do whatever it takes to prevent radioactive water to spread to the building's underground and to the sea.

The Tokyo Electric Power Co. (TEPCO) said on Sunday that the concentration of radioactive substances in a pool of the number two reactor is 100,000 times higher than allowed limit, and underlined that its earlier analysis showing 10 million times higher radiation was wrong.

The Japanese Nuclear and Industrial Safety Agency (NISA) stated that the concentration of radioactive iodine-131 in a seawater sample taken about 1.5 kilometers north of the drainage outlets of the number 1-4 reactors is 1,150 times the maximum allowable level.

The level of water contamination was 1,850 times the allowed limit on Sunday, while officials announced that sea flora and fauna are not endangered.