SAN FRANCISCO (AP) — Widespread blackouts to reduce pressure on the electric grid were averted Monday night after regulators warned earlier in the day that they would not have enough power to meet demand in the midst of a heat wave.

The California Independent System Operator lifted its emergency declaration shortly before 8 p.m. Monday, after the state’s power grid operator had warned that it expected to implement rotating outages that could have left millions of Californians in the dark for up to two hours.

California ISO would have ordered utilities to shed their power loads as demand for electricity to cool homes soared. The operator had said as many as 3.3 million homes and businesses would be affected but later reduced that to around a half-million before cancelling the option.

Pleas for people to leave their air conditioners at higher temperatures and avoid using washing machines and other major appliances seemed to have worked.

“Thank you for conserving,” California ISO said in a tweet.

The first rolling blackouts in nearly 20 years came Friday as unusually hot weather overwhelmed the electrical grid. The three biggest utilities — Pacific Gas & Electric, Southern California Edison and San Diego Gas & Electric — turned off power to more than 410,000 homes and businesses for about an hour at a time until the emergency declaration ended 3 1/2 hours later.

A second but shorter outage hit Saturday evening, affecting more than 200,000 customers. Californians packed beaches and river banks over the weekend to cool off from scorching triple-digit temperatures that raised the risk of more wildfires and fears of the coronavirus spreading.

Gov. Gavin Newsom signed an emergency proclamation Sunday allowing some energy users and utilities to tap backup energy sources. He acknowledged Monday that the state failed to predict and plan for the energy shortages.

“I am not pleased with what’s happened,” he said during a news briefing. “You shouldn’t be pleased with the moment that we’re in here in the state of California.”

Newsom also sent a letter demanding that the state Energy Commission, state Public Utilities Commission and the California Independent System Operator investigate the blackouts.

The Democratic governor said residents battling a heat wave and a pandemic in which they’re encouraged to stay home were left without the basic necessity of electricity. In Southern California, temperatures reached a record high of 110 in Lancaster and 111 in Palmdale.

“These blackouts, which occurred without prior warning or enough time for preparation, are unacceptable and unbefitting of the nation’s largest and most innovative state,” Newsom wrote in the letter. “This cannot stand. California residents and businesses deserve better from their government.”

During a grid operator board meeting Monday, California ISO CEO and President Steve Berberich said the weekend blackouts could have been avoided had regulators listened to its previous concerns about a power shortfall. In a call later with reporters, he said he knows the Public Utilities Commission is working to find the right balance of energy sources.

“It’s substantial, no question about it,” he said of the outage.

The Public Utilities Commission said it would work with the other agencies to figure out what happened. The demand for electricity in the last few days has been consistent with expectations, spokeswoman Terrie Prosper said.

California also still faces the threat of power outages to prevent wildfires. Thousands were without power for days last year when Pacific Gas & Electric and other utilities shut off lines amid high, dry winds in order to prevent wildfires.

Beam reported from Sacramento. Associated Press writers Olga R. Rodriguez in San Francisco and Christopher Weber in Los Angeles also contributed to this report.