California Governor Gavin Newsom on Thursday announced new statewide bans on gatherings and "non-essential" activities, as hospitals in the nation's most populous state face being overwhelmed by record Covid-19 cases.

The limits will come into effect once capacity in intensive care units hits 15 percent or lower -- a development expected in four of California's five regions "as early as the next day or two."

"We are announcing and introducing a regional 'stay-at-home' order in the state of California, fundamentally predicated on the need to stop gathering with people outside of your household," said Newsom.

Once a region is placed under the new limits, an "emergency brake" which will last for a minimum of three weeks, the gathering of people from different households will be banned. 

Bars, wineries and personal services such as hair salons will be temporarily closed.

"We're also establishing a framework where all non-essential travel is as well temporarily restricted statewide," said Newsom.

California's Bay Area surrounding San Francisco is projected to hit the new limit slightly later than the rest of the state, around mid- to late-December, he added.

Retail occupancy will be limited at 20 percent capacity, while schools with waivers and critical infrastructure will be allowed to remain open. 

California is experiencing record new cases of Covid-19 in a third wave of the virus, with two days this week in which 113 deaths were recorded, up from around 14 daily fatalities in early November.

The state overall has seen more than 1,260,000 cases including over 19,400 deaths.

The measures follow similar bans on gatherings that went into place this week in densely populated and badly hit Los Angeles County.

They extend upon a near-statewide nighttime curfew introduced last month.

"If we don't act now, our hospital system will be overwhelmed," said Newsom.