A video of the inside of the crippled Fukushima Daiichi nuclear power plant's No.1 reactor shows major damage to the base, raising concerns about its ability to withstand future earthquakes.

The No.1 reactor and two others at the power station melted down following the March 2011 earthquake and tsunami.

The operator, Tokyo Electric Power Company, on Tuesday released a video clip showing the inside of the pedestal -- a structure supporting the reactor.

It shot the video in late March by putting an underwater robot into the reactor containment vessel, which is filled with water to cool down the fuel.
The images have white lines caused by radioactive rays, indicating high radiation levels inside the pedestal.

Accumulated matter can be seen at the bottom of the pedestal. It appears to be nuclear debris -- a mixture of molten nuclear fuel and other materials. TEPCO says the accumulation appears to be 40 to 50 centimeters high.

The video also shows that the wall of the pedestal, which is a cylindrical shape, has damage extending halfway round its circumference.

TEPCO says a section of the concrete wall one meter from the bottom has crumbled away, exposing the reinforcing steel bars, some of which are distorted.

The firm has previously said that even if part of the pedestals were damaged, the ability of the plant to withstand earthquakes would not be compromised.

But TEPCO now says the latest video shows the damage may be heavier than expected. It plans to analyze the video to reassess the possible impact.