Extracting the estimated 880 tons of highly radioactive fuel and debris inside the former power station remains the most challenging part of decommissioning the facility, which was hit by a catastrophic tsunami in 2011.

Radioactivity levels inside are far too high for humans to enter and earlier this month engineers began inserting an extendable device to try and remove a small sample.

However, Tokyo Electric Power Company (TEPCO) had to halt the procedure on Tuesday after noticing that remote cameras on the apparatus were not beaming back images to the control centre.

"We are investigating the cause of the problem," TEPCO spokesman Tatsuya Matoba told AFP.

"We need to find out the cause of the trouble before resuming," he said.

TEPCO originally planned to start on August 22, aiming to collect three grams (0.1 ounces) for analysis, but technical problems caused a delay.

Three of Fukushima's six reactors went into meltdown after a tsunami triggered by Japan's biggest earthquake on record swamped the facility in one of the world's worst atomic accidents.

Japan began last year releasing into the Pacific Ocean some of the 540 Olympic swimming pools' worth of reactor cooling water amassed since the catastrophe.

China and Russia banned Japanese seafood imports as a result although Tokyo insists the discharge is safe, a view backed by the UN atomic agency.

In a TEPCO initiative to promote food from the Fukushima area, swanky London department store Harrods began selling peaches grown in the region this month.