Major airlines including British Airways, Ryanair, easyJet and Virgin Atlantic announced a dramatic scaling-back of their operations on Monday, including plans to cancel the majority of their flights and ground thousands of planes, with experts and industry executives calling for government bailouts to avoid bankruptcies.

The moves came as an aviation consultancy warned that the international airline industry will collapse within months, with the loss of hundreds of thousands of jobs, unless states worldwide inject billions of dollars of emergency funding to see it through the coronavirus “catastrophe”.

“By the end of May 2020, most airlines in the world will be bankrupt,” the Centre for Aviation said. “Coordinated government and industry action is needed – now – if catastrophe is to be avoided.

“As the impact of the coronavirus and multiple government travel reactions sweep through our world, many airlines have probably already been driven into technical bankruptcy, or are at least substantially in breach of debt covenants.”

A slew of big airline groups announced capacity cuts of up to 80% and plane groundings on Monday, including American Airlines, United Airlines, SAS, Air France-KLM and Air New Zealand. Some airlines, including Ryanair, Europe’s largest short-haul airline, have said their entire fleets could soon be grounded. Ryanair said on Monday it would reduce capacity by 80% in April and May, while BA’s owner IAG said it would cut by 75% over the same period. EasyJet said it could ground the majority of its fleet, as it said governments might need to step in with financial aid.

Peter Norris, the chairman of Virgin Group,the majority shareholder in Virgin Atlantic, asked the UK government to provide £7.5bn of emergency state support to try to rescue the UK aviation industry.

Virgin Atlantic said it would cut 80% of its flights by 26 March and ground 75% of planes. Its route from London Heathrow to Newark has been terminated with immediate effect. Staff have been asked to take eight weeks of unpaid leave.

In an internal memo seen by the Guardian, Virgin Atlantic bosses told staff that from 26 March it would scale back to a “skeleton fleet of six aircraft” until May. That means the rest of its fleet of 45 planes will be mothballed.

Willie Walsh, chief executive of BA’s parent company, International Airlines Group (IAG), said he was postponing his retirement to help steer the airline through the crisis. He was due to step down as CEO on 26 March.

“The situation is going to be quite dynamic in the next few weeks,” Walsh said. “There are many airlines out there who are severely stressed with little or no cash resources.”

Norwegian Air said it was cancelling 85% of its flights and would temporarily lay off 90% of its staff – 7,300 people. Scandinavian airline SAS is temporarily laying off 10,000 employees, or 90% of the workforce.

The US president has banned all flights to the US from Europe, including the UK and Ireland, for at least a month. Flight restrictions have been put in place by dozens of other nations across Europe and the rest of the world.

Iata, the aviation trade body, had already estimated that the industry would lose up to $113bn in revenue as a result of the crisis. But that estimate was on 5 March, before the true scale of the Covid-19 crisis became apparent and governments acted to close the skies.

Share prices in virtually all airlines have collapsed by more than 50% since the coronavirus crisis struck Europe.

Len McCluskey, general secretary of the Unite union, has called on Boris Johnson to bail out the aviation industry to protect tens of thousands of jobs. “If you do not take urgent action to support the aviation industry in the UK,” he told the prime minister in a letter on Monday, “there is absolute certainty that tens of thousands of jobs will be put at risk, and the industry will be unable to resume effectively once this health crisis has passed.”

The package holiday company Tui has cancelled travel to almost all of its holiday destinations.

“In this rapidly changing environment, the safety and welfare of our guests and employees worldwide remains of paramount importance and thus Tui Group has decided, in line with government guidelines, to suspend the vast majority of all travel operations until further notice, including package travel, cruises and hotel operations,” a spokesman for TUI said.

“This temporary suspension is aimed at contributing to global governmental efforts to mitigate the effects of the spread of Covid-19.”