Image copyright AP Image caption More than 1,000 people spent Monday night at Narita airport outside Tokyo

US airline Delta has cancelled at least 300 more flights after a power cut on Monday that resulted in the cancellation of 1,000 flights and delays for about 2,800 more.

The company has not yet given details about the financial damage.

But correspondents say it is likely to amount to millions of dollars.

The meltdown exposes vulnerabilities in Delta's computer system, which is over-reliant on IT systems that date from the 1990s, correspondents say.

Although the airline was back online late on Monday, it was still dealing with the knock-on effects a day later.

Image copyright AP Image caption Delta's main challenge will be to find sufficient seats on planes during the busy summer holiday season

Image copyright AP Image caption The Atlanta-based airliner says it will pay compensation to customers affected by significant delays or cancellations

Its main challenge will be to find sufficient seats on planes during the busy summer holiday season for tens of thousands of passengers whose flights were cancelled.

The flight tracking service FlightStats said there were nearly 600 delayed flights on Tuesday, with cancelled flights closer to 330.

More than 1,000 people spent Monday night at Narita airport outside Tokyo, with Delta spokeswoman Hiroko Okada warning that more delays were expected. There were similar scenes earlier in the day throughout the US.

"We were able to bring our systems back on line and resume flights within a few hours yesterday but we are still operating in recovery mode," a Delta statement said on Tuesday.

Image copyright AP Image caption The disruption was so severe on Monday that at one point Delta warned passengers that information provided by its employees, website and app may be out of date

The problems began when a switchgear, that helps to control and switch power flows in the same way as a circuit breaker does in people's homes, malfunctioned for reasons that were not immediately clear, experts say.

The Atlanta-based airliner says it will pay compensation to customers affected by significant delays or cancellations.

The meltdown raises questions over a recent wave of four US airline mergers that resulted in four large carriers controlling 85% of domestic capacity, The Wall Street Journal reported.

It says this has resulted in the creation of companies that are too large and too dependent on IT systems that date from the 1990s. Delta merged with Northwest Airlines eight years ago.

Computer systems used by the airlines control everything from flight dispatching, crew scheduling, passenger check-ins, airport departure information and ticket sales.

They are gradually being phased out and updated but remain vulnerable, IT experts quoted by the newspaper said.

The disruption was so severe on Monday that, at one point, Delta warned passengers that information provided by its employees, website and app may be out of date.

The overnight power failure took place in Atlanta, near Delta's headquarters, the company said, causing computer systems to crash.

Many travellers posted their unhappiness on social media, making #Delta a top trending topic.

The airline serves about 180 million customers a year, employing over 80,000 people, its website says.