TEPCO workers remotely operate heavy machinery at the Fukushima Daiichi nuclear plant.

TOKYO--Robots and remote-controlled heavy machinery finally got to work at the crisis-hit Fukushima nuclear plant in an effort to minimize human exposure to radiation as Japan raised the severity of the disaster from 5 to 7, putting it on par with the 1986 Chernobyl catastrophe.

A month after the 9.0-magnitude March 11 earthquake, operator Tokyo Electric Power Company (TEPCO) deployed three remote-controlled excavators equipped with cameras to clear radioactive debris around the unit 3 reactor, according to a TEPCO spokeswoman.

The unmanned machinery was donated by Shimizu and Kajima corporations.

The excavators were donated by two Japanese construction companies. Remote-operated power loaders sent to Japan by Qinetiq North America are still being evaluated before deployment to the plant.

Meanwhile, TEPCO launched a Honeywell T-Hawk micro air vehicle to survey the plant from above. As seen in the video below, the MAV recorded footage of the reactors and turbine structures from about 500 feet up, showing extensive damage to the buildings from the tsunami and hydrogen blasts.

TEPCO has also used two of Qinetiq's portable Talon robots--often used for ordnance disposal and reconnaissance--to take additional footage of the plant and the obstacles preventing the deployment of more machines. The bots have audio and video feeds as well as chemical, biological, radiological, nuclear, and explosive detection kits.

Powerful aftershocks shook Tokyo and northeast Japan again on Monday and Tuesday, temporarily cutting power to the plant, but cooling operations are continuing.

Meanwhile, Japan's Nuclear and Industry Safety Agency raised the severity of the crisis to 7, the highest on the International Nuclear Event Scale (INES).

The Fukushima crisis had been ranked at 5 on the INES, the same level as the Three Mile Island accident. A rank of 7, or "major accident," involves a "major release of radioactive material with widespread health and environmental effects," according to an INES pamphlet.

TEPCO says there are some 900 workers at the Fukushima Daiichi and Daini plants tackling the crisis, but none has exceeded the annual radiation dosage limit of 250 microsieverts. About 20 workers have reached the 100-microsievert level.

Japan also expanded the 12-mile evacuation zone on Monday to include the communities of Katsurao, Namie, and Iitate, as well as parts of Kawamata and Minamisoma. The government has estimated that the radiation dose in part of Namie could exceed 300 millisieverts over a year.

It's another sign that parts of Japan may be permanently abandoned as nuclear wastelands.