Japan earthquake
A second earthquake has hit Japan's southern Kumamoto prefectureKazuhiro Nogi/AFP

A second major earthquake has hit southern Japan barely 24 hours after the powerful tremor that killed nine people in the region. Authorities have issued a tsunami alert, warning of a possible 1-metre wave along the coast in the Kumamoto prefecture on Kyushu Island.

The quake, which was initially rated at 7.4 but later downgraded and then upgraded again,struck at 1.25am local time on 16 April and was centred near Kumamoto city. Its epicentre was at a depth of of 40 kilometres, according to the US Geological Survey.

The death toll currently stands at one, however 23 people are reportedly trapped under rubble. The figures are expected to rise and the United States Geological Service (USGS) said that, based upon their analysis, there was a 56% chance of anything between 1,000 and 10,000 fatalities.

NHK reported that there are now fears that a nearby dam could collapse, forcing the evacuation of residents in the surrounding area. Hundreds of patients have already been evacuated from a hospital in Kumamoto over concerns it could collapse. There are numerous reports of people being trapped inside buildings including 70 elderly men and women in an old people's home. Aftershocks have been felt through the night and as morning breaks, the extent of the damage is now becoming clear.

A day earlier, the area was rattled by magnitude 6.5 earthquake that caused numerous buildings to collapse, injuring some 860 people. It was followed by more than 130 aftershocks before the second, more powerful tremor struck.