Hospitals in the heart of California's Central Valley are running out of beds in their intensive care units (ICUs), state officials say, as a more contagious version of the coronavirus continues to spread primarily among the unvaccinated population.

According to AP, hospitals in the 12-county San Joaquin Valley region have had fewer than 10 per cent of staffed adult ICU beds for three consecutive days. State officials labeled it a surge, triggering special rules announced last month that require nearby hospitals to accept transfer patients.

In Fresno County and neighboring counties, the number of confirmed and suspected coronavirus patients in hospitals is more than double what it was four weeks ago, the Fresno Bee reported.

In San Joaquin County, new virus cases and the number of people admitted to hospitals has surpassed the peak numbers of cases and patients during last summer's surge, according to the county health officer.