There's a high chance of a magnitude-7.0 quake or above in the next three days because of increased tectonic activity, the earthquake prediction department chief for the Japan Meteorological Agency said Sunday.

The Japanese agency canceled all tsunami warnings Sunday, but said more warnings and advisories are likely to be issued because of aftershocks.

The USGS reported scores of such aftershocks. More than two dozen were greater than magnitude 6, the size of the quake that severely damaged Christchurch, New Zealand last month, the agency said.

And the death toll is expected to surge. The number of dead in Miyagi prefecture alone "will undoubtedly be in the tens of thousands," Japanese public broadcaster NHK reported, citing the prefecture's police chief.

Japan plans to dispatch 100,000 members of its defense forces to the quake-ravaged region -- double the previous number -- authorities said Sunday.

"We are extending emergency food, drinks and assistance to affected areas," the prime minister's office said.

At least 48 other countries and the European Union also have offered relief. The nuclear-powered aircraft carrier USS Ronald Reagan arrived off Japan's coast Sunday morning to support Japanese forces in disaster relief operations, the U.S. Department of Defense said in a statement.

Friday's quake is the strongest earthquake in recorded history to hit Japan, according to USGS records that date to 1900. The world's largest recorded quake took place in Chile on May 22, 1960, with a magnitude of 9.5, the agency said.