(Updates deaths, major power outages, evacuations, 10 houses destroyed by bushfares)

By Michael Perry

SYDNEY, Jan 30 (Reuters) - Authorities fear several elderly people may have died in a heatwave baking southern Australia, after 22 "sudden deaths" in Adelaide on Friday.

On Friday night an estimated 300,000 to 500,00 homes were without power in Melbourne as a major outage hit Australia's second largest city, local media reported.

The city grounded to a halt with traffic lights and rail signals failing and a number of city buildings were evacuated, with firemen rescuing office workers trapped in stalled lifts.

Extreme temperatures above 40 degrees Celsius (104 Fahrenheit) have baked Victoria and South Australia states for the past three days, disrupting power and transport and leaving medical services struggling.

Weather officials say if the high temperatures continue until Sunday it will equal the worst heatwave in 100 years.

Of the 22 people who died in Adelaide since midnight Thursday, at least 14 of them were elderly.

"How many of them are associated with the heat is speculative, but it's obviously a high number," South Australia state Health Minister John Hill told local media.

Sudden deaths are those caused by medical conditions such as heart attacks and strokes, said an ambulance official, adding autopsies would determine whether the deaths were heat-related.

"Normally the Ambulance Service would have just a few during a day, so this is a much higher number. So, you've got to draw the conclusion that a lot of them have something related to the effects of heat," Hill told the news.com website.

Melbourne recorded its hottest ever three-day heatwave on Friday, after the temperature hit 43.8 degrees Celsius (110.84 Fahrenheit), the third day above 43 Celsius.

On Friday night, Melbourne was hit by a major power outage, triggered when two 500 kilovolt electricity transmission lines that service much of Melbourne's west lost power, said Australian Associated Press (AAP).

With thousands of people flocking to the beach to escape the high temperatures, which are continuing in the night, lifesavers in Victoria state launched night beach patrols on Friday.

The heatwave was stretching medical services in two states, South Australia and Victoria.

"None of our systems are failing, but we are stretched to our limit and if you are not medically urgent you will be experiencing delays," said Ambulance Victoria head Greg Sassella. The South Australian health controller said hospitals were also coming under pressure to treat people with heat-related stress.

"We're getting quite a few patients coming in with effects from the heat, not so much directly with pure heat-stress, but people with chronic diseases that have flared up because of the ongoing heat," Dr Bill Griggs told local radio.

"All the hospitals are pretty full at the moment, we are coping with it, but it's certainly increased the workload."

Australian Climate Change Minister Penny Wong has said the heatwave was a sign of climate change.

Firefighters in Victoria are battling two bushfires which have burnt some 3,200 hectares of forest, grassland and private pine plantation. Ten houses were destroyed in one fire, but there were no reports of injuries.

Fruit growers in South Australia and Victoria said they were battling to save crops in the heatwave. But so far the heatwave has remained in southern Australia and not moved north towards the country's main wheat and sugar crops. (Reporting by Michael Perry; Editing by David Fox)

AlertNet news is provided by