Guests across the world have been told to leave their accommodation mid-holiday after property rentals firm Sonder suddenly went bankrupt.

The collapse came after hotel chain Marriott terminated its leasing agreement with Sonder, a year after the partnership had been established. It allowed Sonder rooms to be booked via Marriott's various booking platforms and app.

But Marriott said "Sonder's default" had led it to break up with the short-term rentals and serviced apartments firm.

One customer on Reddit said he couldn't get back in to his room where his belongings were, while others shared pictures of themselves carting luggage through the streets, seeking rooms elsewhere.

Sonder rooms can no longer be booked via the Marriott site and app. Marriott said it was helping people who booked via its own platforms but was advising those who booked via a third party to ask for a refund via their credit card issuer.

"Sonder has faced severe financial constraints arising from, among other things, prolonged challenges in the integration of the company's systems and booking arrangements with Marriott International," Sonder said in a statement on its website.

Seen as a rival to Airbnb, which offers alternatives to traditional hotels, Sonder focussed on premium serviced apartments and lodgings.

Founded in Montreal, it operates thousands of rooms in over 40 cities, all of which will now be closing as the firm seeks insolvency proceedings in all territories it operates in.

"We are devastated to reach a point where a liquidation is the only viable path forward," said Janice Sears, Sonder's interim chief executive.

She added its integration with Marriott was "substantially delayed due to unexpected challenges in aligning our technology frameworks", which she said resulted in significant costs.

She said there was a sharp decline in revenue "arising from Sonder's participation in Marriott's Bonvoy reservation system".

Marriott Bonvoy is a booking and rewards system operated by Marriott.

One man said he had received no communication about his cancelled Sonder reservation, that there was no way to contact the firm online, and said it was "causing significant worry".

Rob Goodwin found himself abruptly out of work this week as a result of Sonder's collapse.

Mr Goodwin, a front desk manager at the Sonder The Merchant hotel in New York City's lower Manhattan area, was trying to help a guest extend her stay on Sunday when he encountered an unexpected error in the booking system.

Extension dates were no longer available, even though the hotel was only 80% full at the time.

Shortly after, another guest came downstairs to the front desk and showed him an email from Marriott instructing the guest to vacate the property by the following morning, Mr Goodwin said.

"Leadership ghosted us for quite a while," Mr Goodwin said. He said he and his colleagues were in the dark about the situation for several hours.

Mr Goodwin spent 16 hours at the Sonder property on both Sunday and Monday, to help guests figure out alternative lodging options. He said he was only paid for half of that time.

"It was a mess. It was a huge mess," he said, adding that most guests at his location expressed empathy for him and his colleagues.

Mr Goodwin is now unemployed. But he said he is optimistic that he will find similar work though his relationships with building owners in New York City.

He has an 8-year-old daughter to support, and said "it's too expensive to be dealing with this right now".

Sonder's properties often have no staff and rely on door codes for guest entry. Some people have complained that their codes no longer worked and owners were not immediately available to help them retrieve their belongings.

Many users said the only reason they booked with Sonder was because it seemed reliably "backed" by the well-known Marriott brand - but now felt betrayed.

One user on X said "Marriott has been useless", and wanted to charge him hundreds of dollars a night to rebook him at one of its Courtyard brand hotels.

Marriott said on its website that it didn't charge customer cards itself for Sonder bookings, but would facilitate refunds by coordinating "with the appropriate parties".

Marriott said it has a portfolio of over 9,700 properties with 30 brands in 143 countries, and that its business model includes operating hotels as well as franchising and licensing hotels, residential properties, timeshares and lodging properties.

The BBC has asked for comment from Marriott International and Sonder regarding customers' complaints.