New Zealanders are to be urged to wash dishes by hand and turn off lights as the country teeters on the brink of a power crisis caused by drought.

After two years of dry weather, the level of water in lakes that drive New Zealand's hydroelectric power plants is worryingly low.

The energy minister, David Parker, denied claims the country was facing rolling power cuts but said households would be asked to cut electricity consumption by up to 15% during peak early evening periods unless there was "significant" rainfall soon.

Hydroelectric stations usually produce about 75% of New Zealand's electricity but a lack of rain has reduced that output in recent weeks to 50%. Coal, diesel and gas-fired power plants are trying to make up the shortfall, but more strain is expected to be put on the national grid with the arrival of winter in the southern hemisphere.

Backed by the government, the electricity industry is to launch a TV campaign aimed at domestic, commercial and industrial users.

The prime minister, Helen Clark, said: "I think the advice will be that while it's not an emergency, it is time for people to be turning off lights in rooms they are not using, certainly not leaving the computer on all night, the heated towel rail not on for 24 hours a day."

The last time there was a serious power shortage in New Zealand was in 1992 when businesses were forced to use liquid petroleum gas and diesel. Street lighting was rationed and households endured hot water restrictions.

The public was also asked to save power in 2001, 2003 and 2006 but each time rain came soon enough to head off any serious problems.

Phil O'Reilly, the chief executive of Business New Zealand, said poor decisions by successive governments had led to New Zealanders living with the threat of electricity shortages. "You just can't run an economy like this," he said.

"If we get through to the end of winter without blackouts; it was all done by the skin of our teeth. I don't think that's a sensible proposition."

Clark said the commissioning of a new geothermal plant was being brought forward and industrial users of electricity were being targeted to see if they could ease back on demand. "A lot of things are being done to make sure that we move through this dry spell as smoothly as we can," she said.