Damage estimates released Thursday by the Hokkaido government show tsunami could kill 149,000 people in the event a major earthquake hits off Japan's northernmost main island, surpassing a central government prediction by around 12,000.

But the report also said deaths could be significantly reduced if thorough evacuation measures are swiftly carried out, a conclusion prompting the Hokkaido government to further cooperate with municipalities to prepare for the worst-case scenario.

The estimates factored in damage from a megaquake and resulting tsunami originating in the Japan Trench, which stretches from Hokkaido to east of the Boso Peninsula near Tokyo, and the Chishima Trench, which lies off the Chishima Islands, also known as the Kuril Islands.

The Hokkaido government revised the estimates by including data gathered from geological surveys carried out so far and factoring in details such as specific evacuation routes and their distance from oncoming tsunami.

The central government had predicted in December that up to 199,000 could die across seven prefectures including Hokkaido in the event a massive earthquake occurred along the Japan or Chishima trenches, with 137,000 of the deaths projected for Hokkaido.