The mass beaching of more than 150 melon-headed whales on Japan's shores has fuelled fears of a repeat of a seemingly unrelated event in the country - the devastating 2011 undersea earthquake that unleashed a tsunami and triggered a nuclear disaster.

Despite a lack of scientific evidence linking the two events, a flurry of online commentators pointed to the appearance of around 50 melon-headed whales - a species that is a member of the dolphin family - on Japan's beaches six days prior to the monster quake, that killed around 19,000 people.

Scientists were dissecting the bodies of the whales, 156 of which were found on two beaches on Japan's Pacific coast on Friday, but could not say what caused the beachings.

"We don't see any immediate signs of diseases on their bodies, such as cancer. We want to figure out what killed these animals," Tadasu Yamada, a senior researcher at National Museum of Nature and Science, told public broadcaster NHK.

Despite the lack of any clear link between the beachings and earthquakes and comments from local officials downplaying such a connection, many took to social media to point to the link.

"Is the next one coming? Be ready for a quake," wrote Twitter user maoeos40d.

Another Twitter user wrote simply: "We might have a big one on the 12th [of April]".

The 2011 Japan earthquake was not the only instance of beached whales closely preceding a massive tremor.

More than 100 pilot whales died in a mass stranding on a remote New Zealand beach on February 20, 2011, two days before a large quake struck the country's second-largest city Christchurch.

Japanese officials nevertheless tried to calm fears and insisted there was no scientific data to prove the link.

Scientists are meanwhile unclear as to why the marine animals strand themselves in large groups, with some speculating healthy whales beach themselves while trying to help sick or disorientated family members that are stranded.

Others believe the topography of certain places somehow scrambles the whales' sonar navigation, causing them to beach.

Once stranded, the whales are vulnerable to dehydration and sunburn until rescuers can use the high tide to move their massive weight back into deeper water.

AFP