Rescue units from the Russian Emergency Situations Ministry stand ready to aid Japan after a massive earthquake and tsunami ravaged the country, the ministry said Saturday.

"Instructed by Russian President Dmitry Medvedev, the Emergency Situations Ministry has prepared the necessary forces and resources to provide assistance to Japan. If a relevant decision is made, they will fly to the disaster area," a ministry spokesperson told Interfax news agency.

In particular, six planes, including an airborne hospital, 200 rescuers, psychologists and doctors are ready to fly to Japan, the ministry said.

At least 630 people were killed by the 8.8-magnitude earthquake and the ensuing tsunami in northeastern Japan on Friday. Japan's National Police Agency and the Defense Ministry said at least 725 are still unaccounted for in six prefectures and the number of victims may rise to well over 1,000.