Japanese company Mitsubishi has unveiled a radiation-resistant robot it says can help clean up the crippled Fukushima nuclear power plant.

It joins other companies, including Hitachi and Toshiba, that have introduced their own radiation-resistant remote-controlled robots.

While robots are already at work inside the nuclear plant damaged in the 2011 earthquake and tsunami, none of them is specifically designed to work in a highly radioactive environment, experts said.

Jeremy Pitt of the Intelligent Systems and Networks Group at Imperial College London said such tasks required a robot that could mimic human actions and decision-making.

"Fundamentally, instead of programming a robot to follow a precise series of actions, in open environments the requirement is to program it to improvise," Pitt told the BBC.

Most current robots are designed for different purposes, like clearing bombs or doing rescue and search work.

"If you are wishing to operate robots 24/7 inside a debris-filled power station in a radioactive area, it is much better to design the custom robot from the outset to meet specific tasks," said Mark Clark of Qinetic, a British company whose robots being currently used at Fukushima were designed to search for roadside bombs.