Scorching heat is still severely stretching power supplies in parts of the US, with consumers warned of more shortages unless they reduce demand. The National Weather Service has issued another excessive heat warning for California with temperatures set to reach 44C (111F) in Los Angeles.

The risk of rolling blackouts still remains and a power grid spokeswoman said: "We still have our guard up."

About 29 deaths across the US in recent days are being linked to the heat wave. Electricity is now back on in many of the hundreds of thousands of homes hit by power outages in the past few days, including in California and New York.

But in Queens in New York, about 1,000 customers were still without power for a ninth day on Tuesday, a utility company told the Associated Press news agency. Consolidated Edison said its engineers were working around the clock to restore its services. By late on Monday, more than 150,000 people still had no electricity in St Louis, Missouri, where supplies were knocked out last week by storms.

Tens of thousands of homes and businesses also lost supplies in recent days because of heavy electricity use and high temperatures that caused transformers and other equipment to break down. Monday saw demand for electricity rise to a record high in California, stretching the power grid, California Independent System Operator (Cal ISO) to the limit but rolling blackouts were averted.

"It looks like we dodged a bullet," said Gregg Fishman, Cal ISO spokesman, told Reuters news agency. The power grid and utility companies said they would again ask businesses and consumers to conserve power to help avoid disruptions.

"Conservation is absolutely necessary. It's not just key or guidance. It is absolutely necessary if we are going to avoid rolling blackouts," Marlon Walker of Southern California Edison told Reuters.