Businesses are still counting the cost of the blackout

Power plants knocked out by the outage were coming back online, increasing the electricity flow in time for all of the expected power demands, the Associated Press reported.

"The subways are working, the buses are working," Mayor Michael Bloomberg said on cable news channel NY1. "It's a Monday morning in New York; that's what you'd expect."

In Canada, the premier of Ontario, Ernie Eves, appealed to people to cut electricity consumption in half until electricity supplies were stable.

Investigators are focussing on transmission faults in Ohio as the likely cause of the blackout, which left about 50 million people without electricity for nearly 30 hours.

Shares rise

Financial markets were relieved that business appeared to be getting back to normal.

The Dow Jones stock index rose 90 points to 9,412 during the day, its highest level for 14 months.

What a blessing! I got to see the stars from my own roof like nothing before, a trip across town with friends was a pure adventure, and my university exams got cancelled. ST, Toronto Power cuts: Were you affected?

Trade on the New York Stock Exchange had virtually ground to a halt on Friday, with few dealers getting to work even though the markets were open.

Investors were also relieved by news from the US' largest retailer, Wal-mart, which said sales would rise this month despite the blackout.

In Detroit, Michigan, the big three US car manufacturers told employees to report to work on Monday, after several plants were forced to close on Friday.

But thousands of small firms and restaurants are still counting the cost of wasted produce and struggling to restock their shelves.

And in Canada, Mr Eves, who has declared a state of emergency in Ontario province, said only those government employees who work in essential services should report for work.

Ontario has urged big power uses such as manufacturers or car makers to halve their electricity usage, and Ford was amongst the firms to stop the day production shift at its Oakville, Ontario factory.

Living with uncertainty

Mr Eves has also urged people to avoid using power-guzzling equipment like air conditioners, dishwashers and washing machines.

"We currently do not have enough generation back on line to see us through a regular weekday," Mr Eves told reporters.

Officials in the US and Canada have warned of the possibility of rolling blackouts.

"On Monday, millions of New Yorkers will set foot back in the subways," said New York state governor George Pataki.

Click here to see a map of the north American electrical grid Enlarge Map

"We know that our system will be up and running, but we cannot say with 100% certainty that this can't happen again, until we know what happened and what steps are being taken to prevent it again."

A top US energy official said it could be several days until the exact cause of the blackout was known, and warned of more power cuts.

"We're not out of the woods yet," Pat Wood, chairman of the Federal Energy Regulatory Commission, told NBC's Meet the Press programme.

In Detroit, Michigan, there were no reported blackout-related problems on the city's highways.

The US and Canada are setting up a joint taskforce to find out what caused the power failure, which shut down parts of their inter-connected grid within three minutes.

US President George W Bush has said the blackout was a "wake-up call" to modernise an antiquated system.