Water contaminated with high levels of radioactive material from a wrecked Japanese nuclear plant is set for release into the Pacific Ocean, a UK newspaper claims.

Japan is running out of space to hold 2 million tonnes of the water that was fouled by radioactive fuel during the 2011 Fukushima Dai-Ichi nuclear plant disaster.

The material leaked from three reactors when the plant was destroyed by an earthquake and subsequent tsunami.

The Japanese government insists nearly all radioactive materials in the water are at “non-detect” levels.

But the newspaper reports it has seen leaked government documents that contradict this.

Some of the 900 storage tanks that contain the contaminated water. (AP)

Both the plant’s owners - Tokyo Electric Power Company (Tepco) – and the government have declared the water safe.

Tepco maintains the only major contaminant in the water are legally acceptable levels of tritium.

The substance is found in small amounts in drinking water but is potentially dangerous in larger doses.

The government declared its analysis of the water using the Advanced Liquid Processing System (ALPS) showed all other radioactive material present is at “non-detect” levels.

But the UK Telegraph claims it has been handed government documents that reveal the ALPS failed to detect other radioactive elements such as iodine, ruthenium, rhodium, antimony, tellurium, cobalt and strontium remain.

Nuclear experts inspect one of the Fukushima nuclear reactors last year. (AP)

Another file passed to the newspaper indicated authorities realised the ALPS process was not reducing radionuclides to “non-detect” levels.

It added to a study by the Kahoko Shinpo newspaper in Japan which established that levels of two carcinogenic substances - iodine 129 and ruthenium 106 - surpassed acceptable amounts in 45 samples out of 84 last year.