Alphabet-owned Waymo has resumed its driverless ride-hail service in the San Francisco Bay Area after a temporary pause during blackouts that plagued the city beginning on Saturday afternoon.

"Yesterday's power outage was a widespread event that caused gridlock across San Francisco, with non-functioning traffic signals and transit disruptions," a Waymo spokesperson, Suzanne Philion, told CNBC in an e-mailed statement Sunday afternoon.

"While the failure of the utility infrastructure was significant, we are committed to ensuring our technology adjusts to traffic flow during such events," she added.

As power outages spread yesterday, videos shared on social media appeared to show multiple Waymo vehicles stalled in traffic in different parts of the city.

San Francisco resident Matt Schoolfield said he saw at least three Waymo autonomous vehicles stopped in traffic Saturday around 9:45 p.m. local time, including one he photographed on Turk Boulevard near Parker Avenue.

"They were just stopping in the middle of the street," Schoolfield said.

The power outages began around 1:09 p.m. Saturday and peaked roughly two hours later, affecting about 130,000 customers, according to Pacific Gas and Electric. As of Sunday morning, about 21,000 customers remained without power, mainly in the Presidio, the Richmond District, Golden Gate Park and parts of downtown San Francisco.

PG&E said the outage was caused by a fire at a substation that resulted in "significant and extensive" damage, and said it could not yet provide a precise timeline for full restoration.

San Francisco Mayor Daniel Lurie said in a 9 p.m. update on X that police officers, fire crews, parking control officers and city ambassadors were deployed across affected neighborhoods.

Waymo's Philion also told CNBC that "While the Waymo Driver is designed to treat non-functional signals as four-way stops, the sheer scale of the outage led to instances where vehicles remained stationary longer than usual to confirm the state of the affected intersections. This contributed to traffic friction during the height of the congestion."

Waymo "closely coordinated with San Francisco city officials," she said, and proactively paused its service as of Saturday evening and in the first half of the day on Sunday.

"The majority of active trips were successfully completed before vehicles were safely returned to depots or pulled over," she noted.

Amid the disruption, Tesla CEO Elon Musk posted on X: "Tesla Robotaxis were unaffected by the SF power outage."

Unlike Waymo, Tesla does not operate a driverless robotaxi service in San Francisco.

Tesla's local ride-hailing service uses vehicles equipped with "FSD (Supervised)," a premium driver assistance system. The service requires a human driver behind the wheel at all times.

According to state regulators — including the California Department of Motor Vehicles and California Public Utilities Commission — Tesla has not obtained permits to conduct driverless testing or services in the state without human safety supervisors behind the wheel, ready to steer or brake at any time.

Tesla is vying to become a robotaxi titan, but does not yet operate commercial, driverless services. Tesla's Robotaxi app allows users to hail a ride; however, its vehicles currently have human safety supervisors or drivers on board, even in states where the company has obtained permits for driverless operations.

Waymo, which leads the nascent industry in the West, is Tesla's chief competitor in AVs, along with Chinese players like Baidu-owned Apollo Go.

The outage-related disruptions in San Francisco come as robotaxi services are becoming more common in other major U.S. cities. Waymo is among a small number of companies operating fully driverless ride-hailing services for the public, even as unease about autonomous vehicles remains high.

A survey by the American Automobile Association earlier this year found that about two-thirds of U.S. drivers said they were fearful of autonomous vehicles.

The Waymo pause in San Francisco indicates cities are not yet ready for highly automated vehicles to inundate their streets, said Bryan Reimer, a research scientist at the MIT Center for Transportation and co-author of "How to Make AI Useful."

"Something in the design and development of this technology was missed that clearly illustrates it was not the robust solution many would like to believe it is," he said.

Reimer noted that power outages are entirely predictable. "Not for eternity, but in the foreseeable future, we will need to mix human and machine intelligence, and have human backup systems in place around highly automated systems, including robotaxis," he said.

State and city regulators will need to consider what the maximum penetration of highly automated vehicles should be in their region, Reimer added, and AV developers should be held responsible for "chaos gridlock," just as human drivers would be held responsible for how they drive during a blackout.

— CNBC's Riya Bhattacharjee contributed reporting.