Fukushima disaster: What happened at the nuclear plant?

Ten years ago, on a Friday afternoon in March, the most powerful earthquake ever recorded in Japan struck off the country's eastern coast.

The 9.0-magnitude quake was so forceful it shifted the Earth off its axis. It triggered a tsunami which swept over the main island of Honshu, killing more than 18,000 people and wiping entire towns off the map.

At the Fukushima nuclear power plant, the gigantic wave surged over defences and flooded the reactors, sparking a major disaster. Authorities set up an exclusion zone which grew larger and larger as radiation leaked from the plant, forcing more than 150,000 people to evacuate from the area.

A decade later, that zone remains in place and many residents have not returned. Authorities believe it will take up to 40 years to finish the work, which has already cost Japan trillions of yen.