Cinema booking websites crashed after large numbers of Avengers fans tried to buy tickets for the next instalment of the superhero series.
Odeon and Cineworld suffered outages due to a surge in demand prompted by the release of tickets to screenings of Avengers: Endgame.
Odeon said it was experiencing “incredibly high traffic volumes” and asked fans to “bear with us”.
Vue experienced similar problems, asking fans to “please be patient” as the company attempted to get their website back online.
In a post to social media it said: “We’re experiencing high levels of demand for Avengers: Endgame tickets.
“If you have our iOS app please try through there, if not please be patient and bear with us on this, you’ll be able to book your tickets soon!”
Vue established a queuing system with reported wait times of more than an hour.
The rush came after Anthony Russo and Joseph Russo, the sibling directorial team behind the movie, posted on Twitter announcing tickets had gone on sale.
They shared a quote from the movie, which read: “It’s not about how much we lost, it’s about how much we have left.”
Fans were not impressed, with many taking to social media to complain.
Others who had been successful in acquiring tickets celebrated. One fan said: “Raise your hands if you’ve gotten your tickets!”
One user joked they felt like the supervillain Thanos from the series, writing: “How I feel now that I got my Avengers: Endgame ticket.”
Avengers: Endgame will follow on from the events of Avengers: Infinity War and will be released in UK cinemas on April 25.