Some flights at Heathrow have resumed after the airport was shut on Friday due to a fire at a nearby electrical substation that supplies it with power.
The UK's busiest airport has warned of significant disruption over the coming days, with at least 1,300 flights in and out cancelled.
What are your rights if your journey has been disrupted and can you get your money back?
Do not attempt to travel to the airport, but keep in touch with your airline who will be able to advise you about refunds or booking alternative flights.
If your flight is covered by UK law, your airline must let you choose between either getting a refund or being booked on to an alternative flight.
You can get your money back for any part of the ticket you have not used.
So if you booked a return flight and the outbound leg is cancelled, you can get the full cost of the return ticket refunded.
If you accept a refund, your airline has no further duty of care to you. If you need to make any other arrangements, you will need to do so yourself.
If you still wish to travel, your airline is obliged to get you on a new flight as soon as possible, including with rival carriers from alternative airports.
Bear in mind though, with so many flights cancelled, other airports will be stretched as well.
If there are other suitable modes of transport, such as the train for domestic journeys, then you have a right to be booked on to that alternative transport instead.
If your flight was coming into Heathrow on a non-UK airline, then you should check the terms and conditions of your booking.
If you are stuck abroad or at the airport, your airline is obliged to offer you further assistance, including:
If your airline is unable to arrange assistance, you have the right to organise this yourself and claim back the cost later.
The Civil Aviation Authority advises people to keep receipts and not spend more than necessary.
In this instance you will not be entitled to extra compensation from your airline as the situation will be deemed an "extraordinary circumstance" beyond the airline's control.
If your travel insurance policy includes trip disruption, you should be covered if you have to cancel your travel plans.
The Association of British Insurers advises you to check your policy details and speak to your insurer if you're not sure what is included. You may be able to recoup other expenses such as car hire or airport parking fees.
Any bookings made through a credit card may also have recoverable costs.
If you booked a package holiday with a company that is a member of ABTA, the association of travel agents and tour operators, and your flight is cancelled, you are entitled to a suitable alternative flight or a full refund.
In this situation, your airline would usually try to keep passengers on the plane, or failing that set up a holding area in the airport terminal that doesn't require you to enter the country.
If the delay is long enough that passengers cannot be held in the terminal before immigration, they would usually be bussed to a nearby hotel.
Typically they wouldn't be asked to pay for any visa that is issued, such as a port visa or a visa on arrival, according to the consumer group Which?.
However, you should be particularly mindful if your flight cancellation means you end up overstaying somewhere on an existing visa.
Which? warns that, especially in places like the US and China, you should contact local immigration officials and ask for an emergency extension.
Heathrow says it hopes to run a full operation on Saturday, but it has warned customers to expect "significant disruption over the coming days".
Keep in touch with your airline for further information.
The disruption is likely to affect other airports as well as flights are being diverted.
When heavy snow closed Heathrow's runways for a day in December 2010, it resulted in more than 4,000 flights being cancelled over five days.
You are entitled to the same assistance at the airport as for a cancellation if your flight is delayed by more than:
If you are delayed by more than five hours and no longer want to travel, you can get a full refund.
Flights around the world are facing disruption after a fire at a nearby substation caused a power outage at the airport.
People in Hayes share how a fire at an electrical substation that brought Heathrow to a halt affected them.
Travellers are grappling with cancelled flights and face days-long delays in some cases to get home.
Heathrow Airport will be closed all day Friday after a fire at a nearby electrical substation.
The Met says there is "currently no indication of foul play" but officers are keeping an open mind.
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