The death toll from Friday's large earthquake and subsequent tsunami is likely to rise beyond 10,000, Miyagi prefecture's police chief said on Sunday, according to Kyodo News.

Meanwhile Japanese officials were attempting to prevent overheating at the Fukushima No. 1. Nuclear power plant along the eastern coast about 60 miles south of hard-hit Sendai.

The official death was 1,597 as of late Sunday.

Japanese Prime Minister on Sunday called the current situation the toughest crisis facing Japan in 65 years since World War II.

Reports said on Sunday that the United States had sent in the aircraft carrier USS Ronald Reagan to assist.

The Japanese military had also mobilized 100,000 troops to help with relief efforts.

Friday's quake, whose epicenter was off the northeast coast of the country, was the 5th largest since the early 20th century. The Japanese Meteorological Society on Sunday upgraded the magnitude of the quake to 9.0. It had originally been classified as 8.8, and later 8.9 on the Richter Scale.

Meanwhile, seeking to avert a meltdown, Japanese officials injected seawater into overheating nuclear reactors on Sunday, relieving pressure at a nuclear plant in Fukushima prefecture, according to Kyodo News.

The No. 3 reactor at the Fukushima No. 1 plant may have been deformed due to overheating, Chief Cabinet Secretary Yuko Edano said.

He denied that there had been a meltdown at the plant. Such a condition occurs when nuclear fuel rods melt in the reactor.

He also said another hydrogen explosion could take place at another reactor in the facility, similar to one on Saturday that blew off part of the building which housed another reactor at the same plan.

The reason is that large amounts of hydrogen formed when a water injection procedure ran into some temporarily problesm that may have filled part of the building housing reactor No. 3, Edano said.

Plant operator Tokyo Electric Power Co. began injecting water into the No. 3 reactor's core vessel on Sunday, according to the report. 

An evacuation area of 12 miles around the plant has been in place since Saturday, after bein expanded from 6 miles.