Japan has issued a warning of a potential megaquake following a magnitude 7.5 tremor that struck the northern regions late Monday, triggering tsunami alerts.

A powerful earthquake striking the Cascadia subduction zone could lead to a sudden and dramatic rise in sea levels along the Pacific Northwest, posing a major threat to coastal communities from northern California to Washington, according to a new scientific study.

Japan's economy could lose as much as $1.81 trillion in the event of a long-anticipated megaquake off its Pacific coast, which could trigger devastating tsunamis, the collapse of hundreds of buildings and potentially killing about 300,000 people, a government report said on Monday.