Hundreds of thousands of flights could be axed worldwide and airlines go under if the jet fuel crisis continues into the summer, an aviation expert warned today. 

Passengers are already facing higher fares after the cost of jet fuel doubled since the start of Donald Trump's war with Iran. 

The conflict prompted Iran to close the Strait of Hormuz, a key route for jet fuel out of the Gulf. 

It remains off limits to shipping, prompting the International Energy Agency (IEA) to warn that Europe faces possible shortages in six weeks. 

The International Air Transport Association (IATA), which represents more than 360 airlines, has warned passengers to expect flight cancellations in the May half-term holidays as flight disruption spread from Asia to Europe.

IATA director-general Willie Walsh described the IEA's warning as 'sobering'. He added: 'We have also estimated that by the end of May, we could start to see some cancellations in Europe for lack of jet fuel. This is already happening in parts of Asia.'

Sally Gethin, an aviation specialist, said the scale of the impact on air passengers will depend on how long the Strait remains closed. 

'Even if it opens you'd still need time for the jet fuel supplies to start up again,' she told the Daily Mail. 'So the best case scenario would be fares going up and some routes being cancelled. 

'The worst case scenario is if this carries on for six to eight weeks and the shortages start really biting. This could pose an existential crisis to airlines - even if they slap on fuel surcharges they still won't recoup the cost.

'You could be looking at tens of thousands, potentially hundreds of thousands, of flights being cancelled globally. It could affect holiday companies as well, although consumers will be protected if their trips are covered by ATOL.' 

Ms Gethin predicted that smaller airports with less jet fuel storage would be hit hardest, while flights on routes that had only been recently launched by airlines were most liable to cancellation. 

She suggested the end result of the jet fuel crisis could be a situation similar to the 1990s when air travel was more expensive and there are fewer low-fare airlines than today, although she stressed the situation was rapidly evolving and hard to predict. 

German carrier Lufthansa said today that a regional subsidiary, Lufthansa CityLine, will suspend operations from Saturday due to high kerosene prices and labour disputes.

And Dutch airline KLM has cancelled 160 flights across the next month as a result of rising fuel costs. 

Seven other airlines have announced cuts to flights so far. They are British Airways, Virgin Atlantic, United Airlines, Scandinavian Airlines, Cathay Pacific, Air New Zealand and Norse Atlantic Airways.

It comes as officials are war-gaming for shortages sparked by the Iran war as early as the late May bank holiday, threatening thousands of families' getaway plans just as the peak season starts.

They are already facing higher fares because the cost of jet fuel has doubled since the conflict started, which airlines are passing on to their customers.

Holidaymakers could also be hit with queues of up to four hours at some European airports, because of new border controls introduced by Brussels.

IEA boss Fatih Birol sounded the alarm over jet fuel toady by saying Europe faces possible shortages in six weeks.

He warned that flights may 'soon' start being cancelled if oil supplies remain patchy. 

Alluding to the Strait of Hormuz – through which a fifth of the world's oil travels – not yet being fully re-opened, he said: 'I can tell you soon we will hear the news that some of the flights from city A to city B might be cancelled as a result of lack of jet fuel.'

He added that Europe has 'maybe six weeks or so [of] jet fuel left'.

European capitals have been strategising over the potential supply issues after the Continent's trade body for airports first warned last week that jet fuel shortages could be just weeks away.

Airports Council International (ACI) Europe said its members had 'increasing concerns' about the availability of jet fuel, warning smaller airports are particularly vulnerable.

And yesterday it emerged UK ministers are war-gaming for potential shortages in around five or six weeks' time.

Officials believe less than 10 per cent of flights would have to be cancelled if shortages hit, because British suppliers have adapted well and 'diversified' where they buy the fuel from.

They have told airlines they must give passengers at least two-weeks' notice of any cancellations.

However, this could still affect thousands of expectant fliers as the summer holiday high season ramps up.

Airline passengers were left vomiting and passing out after being stranded at Milan Linate airport on Sunday due to Brussels' new border rules for holidaymakers from non-EU countries, known as the Entry/Exit System (EES).

This automated digital border technology is designed to vet tourists when they arrive and leave.

But there are fears of repeat scenes this summer – and that some European airports will not be able to cope with higher passenger numbers in the peak season, after the system became fully operational last week.

Thomas Reynaert, a Vice President of global industry body IATA, said: 'We are very concerned about the lack of progress in resolving problems with the EES.

'Unless there is action to ensure borders are adequately manned and the electronic gates and remote app are working properly, we could see passengers, including families with kids, queuing up to four hours in popular holiday destinations.'

When asked about the possibility of cancellations because of jet fuel shortages, the Editor of Which? Travel, Rory Boland, said: 'If a package holiday or a flight is cancelled then you should get a refund, although you might lose out if you had a hotel booked separately from the flight.

'It is always safer to book a package, otherwise you are left relying on travel insurance which often has unexpected loopholes.'

Airlines UK, which represents major carriers such as British Airways, easyJet and Ryanair, said: 'We are talking to the Government about crucial measures that will be needed to support aviation in the event of fuel disruption.'

It added that there was 'currently' no disruption to jet fuel supplies.

A Government spokesman said: 'We continue to engage with British airlines to support their operations against the backdrop of war in the Middle East, and to limit the impact on passengers.'

It also emerged yesterday that air ambulances would be prioritised under 'worst case scenario' planning for jet fuel shortages.

According to sources familiar with shortages planning, if our supplies were to completely dry up, emergency services craft – including air ambulances and lifeguard and police helicopters – would be prioritised for receiving the fuel.

But Paul Charles, CEO of luxury travel consultancy The PC Agency, warned: 'Demand to fly is at record highs so it's concerning that airlines may need to pull some flights by the late May bank holiday.

'Even if the war ended tomorrow, there would be a huge fuel gap to fill before new supplies come through. That gap simply can't be filled from other areas... and so it's likely that long-haul flights in particular would be affected quite severely.'

Mr Charles explained: 'Airlines will not be able to guarantee fuel at their destination, so won't be able to fly in, for fear of being stranded.'