California has announced sweeping statewide water restrictions for the first time in history to combat the region's devastating drought, the worst since records began.

Governor Jerry Brown issued the declaration at a press conference in a parched, brown slope of the Sierra Nevada mountains that would normally be covered by deep snow.

"Today, we are standing on dry grass where there should be five feet (1.5 metres) of snow," Brown said. "This historic drought demands unprecedented action."

The executive order aims to achieve a 25 per cent reduction in water usage across cities and towns throughout California by a combination of measures.

The order also sets out new measures to reduce water use, including the replacement of 4.6 million square metres of lawns with drought-tolerant landscaping.

A statewide consumer rebate program will also be set up to encourage individuals to replace old appliances with modern, water and energy efficient models.

The measure orders campuses, golf courses, cemeteries and other large consumers of water to significantly cut use.

New homes and developments will also be banned from using potable water for sprinkler systems unless water-efficient drip irrigation systems are used.

Brown has already declared a state of emergency in California over the crippling four-year drought, the most severe on record.