Hundreds of thousands of tiny crabs have been washing up on Southern California beaches as warm ocean currents carry them farther north and closer to shore than usual.

The red tuna crabs have been dying in hordes on beaches from San Diego to Orange County, although some have been washed back out to sea alive.

Such strandings take place periodically and are not necessarily a threat to the species.

The plankton-eating crabs, native to the waters of the Gulf of California, Baja California and the California Current, are 2.5-7.6 cm long and resemble tiny lobsters.

Experts have cautioned people not to eat the crabs because the creatures may have ingested toxin-producing phytoplankton.

Scientists have noted the presence of a toxic algae bloom in the Pacific Ocean stretching from California north to Washington state that might be the largest ever detected off the US West Coast.