A state of emergency was declared Wednesday in parts of westernmost Canada after effluent from a gold and copper mine tailings pond spilled into Rocky Mountains waterways.

Spill estimates doubled since Monday when an earthen dam breach at the Mount Polley Mine sent waste water and mining debris from the pond into nearby pristine rivers and lakes.

Up to 10 million cubic metres of water and 4.5 million cubic metres of fine sand are estimated to have poured into Polley Lake, Hazeltine Creek and Quesnel Lake, said officials.

"The Caribou Regional District has declared a state of local emergency as a result of the Mount Polley tailings pond breach in order to access additional capacity that may be necessary to further protect the private property and government infrastructure in the town of Likely," said a government statement, following a helicopter flyover of the disaster zone to assess the potential environmental damage.

People living in or travelling through the affected area were warned not to drink or bath in water in this region, which is popular with sport fisherman, is a major breeding ground for salmon, and is upstream of the mighty Fraser River, which flows through Vancouver into the Pacific Ocean.

The water ban includes "water recreational activities, drinking, cooking, bathing etc. Only use bottled water until further notice," said the notice.

Pets and livestock were also included in the water ban.

Imperial Metals Corporation, which operates the mine, said it does not know what caused the dam breach, but added that it has been stabilized and is being investigated.

Local media said the four-kilometer wide tailing pond contained mercury, selenium, arsenic, lead, and cadmium.