(CNN) - Hundreds of thousands of travelers are facing a nightmare scenario this week, with the collapse of tour operator Thomas Cook leaving them stranded abroad.
All flights and vacations booked through the company have been canceled, and all retail stores closed.
Around 600,000 travelers are affected, and the countries with the most stranded tourists are Spain, Turkey, Tunisia and Greece.
In Germany, one of Thomas Cook's biggest markets, state-owned broacaster Deutsche Welle reports that insurance companies will help repatriate 140,000 stranded German customers.
Thomas Cook France reports that around 10,000 French customers are currently on vacation and an emergency number (01 45 05 40 81) has been set up to offer advice.
Virgin Atlantic has tweeted that they're helping to bring Thomas Cook passengers and staff home from Cuba, Jamaica and the United States. A US phone number (+1 888 747 7477) has been set up for customers currently in LA, San Francisco, Las Vegas or New York.
The UK government and Civil Aviation Authority (CAA) says a massive repatriation operation has been launched to bring over 160,000 UK travelers home.
Codenamed Operation Matterhorn, it's been dubbed the UK's biggest ever peacetime repatriation.
Here's what affected travelers need to know.
I'm currently on a Thomas Cook holiday. How do I get home?
The CAA will arrange return flights for ATOL-protected travelers currently abroad who were planning to fly back to the UK with Thomas Cook.
What is ATOL? It stands for "Air Travel Organiser's Licence" -- a UK financial protection scheme that safeguards most air package holidays sold by travel businesses that are based in the UK.
Basically, it prevents travelers from being left without assistance or facing a financial loss if their travel company stops trading. Which is exactly what happened in the UK on Sunday.
For those currently abroad and due to fly back to the UK with Thomas Cook, the CAA is providing new flights to get them home.
"Depending on your location, this will be either on CAA-operated flights or by using existing flights with other airlines," says the statement.
"Where possible we are aiming for these to be as close as possible to your original return time and date. Different repatriation arrangements are being made for different locations...In a small number of cases, passengers may be asked to book your own return flights on existing flights with other airlines and claim the cost of this back."
The UK Foreign Office has tweeted that because of a limited number of aircraft, it is "prioritizing passengers in areas with limited alternative options."
"We are doing all we can to get passengers home who can no longer travel on Thomas Cook services," it added.
For specific info on new flights, go to the CAA's "guidance by destination" web page, which offers a table of departure airports you can select from for information about your new flight.
"If we have provided a repatriation flight for you and you make your own arrangements to return to the UK without authorization from the Civil Aviation Authority, you will not be able to reclaim the cost of those alternative arrangements unless there are exceptional circumstances," says the CAA.
Travelers returning after October 6 will have to book their own flights back. But, if you are ATOL-protected you will be reimbursed for the cost of your new flight.
Condor, a German airline owned by Thomas Cook, will continue flight operations, it said in a press release.
"Condor continues to operate as a German company. In order to prevent liquidity constraints Condor has applied for a state-guaranteed bridging loan, which is currently under review by the Federal Government," said the release.
For non-British travelers, if you've got travel insurance, check in with the company as soon as you can. Hold on to all your receipts and documents, as you'll need them for the insurance claim process.
Familiarize yourself with your rights. If you booked via a travel agency or a partner airline, you might be liable for a refund, depending on whether flights are covered by travel insurance.
It's worth checking to see if other airlines will help -- but don't assume you'll get any discounts. Other carriers have no responsibility to honor tickets on failed airlines -- but they might still be able to step up.
If you're on the phone with a travel or insurance representative, remember to be pleasant and polite -- venting your frustration won't get you anywhere.
What about hotels?
Now for the bad news: Travelers who only booked hotels through Thomas Cook and not flight-inclusive packages will have to foot the hotel bill themselves.
But if your Thomas Cook holiday included flights, there is specific advice about accommodation.
The CAA says that if you are currently abroad on an ATOL-protected package holiday with Thomas Cook -- or any company part of the Thomas Cook Group -- the authority "will seek to guarantee your stay directly with your hotel."
"If you are experiencing difficulties with your ATOL-protected hotel, or your hotel is requesting payment from you, please call +44 1753 330 330."
The CAA says it may take a few days to secure these arrangements. In the meantime, do not make a payment to your hotel unless instructed otherwise by the CAA team.
"If our guarantee is not accepted by the accommodation provider, we may need to relocate you to another hotel for the duration of your stay," says the CAA's guidance.
"In these circumstances, the CAA will inform other suppliers, such as transfers, of the change to your accommodation and flight details."
If you are not ATOL-protected, the CAA says you can't make a claim for out-of-pocket expenses and additional nights of hotel accommodation -- but you may be able to claim from your travel insurer, bank or your credit card issuer.
How do I know if I'm ATOL-protected?
"If your flight or holiday is ATOL-protected, you should have received an ATOL Certificate as soon as you made any payment towards the booking, either by email or by post," says the CAA.
If you did indeed receive an ATOL Certificate, look at the "Who is protecting your trip?" section.
"If the company stated on your ATOL certificate is not part of the Thomas Cook Group you should contact that company directly to seek advice on your booking," say the authority.
I haven't traveled yet. How do I get a refund?
Don't bother going to the airport. All Thomas Cook flights were immediately canceled following the announcement of the company's shutdown.
As for getting a refund, again, in the UK it all comes down to ATOL. If your holiday was protected, you should be able to file a claim via the ATOL scheme.
Now here's where things get a bit tricky.
The CAA says if you booked a holiday with Thomas Cook but your flights are with an airline unrelated to the Thomas Cook Group, your flights may still be available.
"You are advised to check with the airline if you are still able to travel," says the authority's advice.
"If you wish to travel, you can do so and make a claim to ATOL for the cost of replacing your other travel services. You are not obliged to use your flights and can instead claim a refund under the ATOL scheme."
As a general rule, it's best to pay for your flights with a credit card, as it will mean you're better protected if the travel company goes bankrupt.
"Various countries have rules that make credit cards, not debit cards liable. So it's worth calling your credit card company and asking them," advises CNN anchor and aviation expert Richard Quest
Francesca Street contributed to this report.