The water supply to tens of thousands of households near Tokyo was cut off Saturday after local checks found it was contaminated with a cancer-causing chemical.

The city of Noda, some 30 kilometres (20 miles) from central Tokyo, said it had stopped supplies to a major part of the city. Most of the neighbouring city of Kashiwa also has no tap water supply.

Water supplies have been cut to a total of 210,000 households in Chiba prefecture, where the two cities are located, according to Jiji Press news agency.

Television footage showed residents queuing up with plastic containers to get water from trucks sent by the cities. Authorities have not determined the cause of the contamination although reports said industrial wastewater was suspected.

Authorities in Chiba and Saitama prefectures, which both neighbour Tokyo, found water taken from the Tone River or one of its branches was contaminated with higher than allowed levels of formaldehyde.

Formaldehyde is a colourless chemical with a pungent odour, classified as a human carcinogen by the Lyon-based International Agency for Research on Cancer.

Chiba stopped taking water from a branch of the Tone River after detecting elevated levels of formaldehyde.

The worst reading was seen in Saitama, which temporarily stopped taking water at a filtration plant that on Friday detected contamination of 0.200 milligrams of formaldehyde per litre (1.06 quarts), more than two times the 0.080 milligram national limit.

Water intake was resumed in Saitama Saturday as the level significantly dropped below the limit, according to prefecture officials.

"The water poses no health risks," local waterworks official Akiyoshi Fujimura said, noting none of it had been supplied to households and that the threshold itself was set on the assumption of consumption over a long period.

"We had hardly detected formaldehyde in check-ups before... We have to find the cause," he told AFP by phone, adding waste water from a factory could be responsible.