West End hits The Lion King and The Life of Pi are among a number of shows that have been forced to cancel performances due to Covid-19 outbreaks.
The Lion King called off shows on Tuesday and Wednesday due "to Covid-enforced absences" among cast and crew.
Life of Pi at Wyndham's Theatre pulled five shows from 9 to 13 December.
The Royal Shakespeare Company's Comedy of Errors at the Barbican in London has also cancelled all performances until 22 December due to Covid cases.
The company said scrapping performances "was a last resort".
The National Theatre had to scratch Monday's preview of its Christmas show Hex after one of its lead actors caught Covid.
The play, based on Sleeping Beauty, has now postponed its press night from Wednesday to 21 December.
In a letter to critics, artistic director Rufus Norris wrote: "You will no doubt be aware of the impact that Covid has been having on productions across the industry (none of ours over the last year have escaped entirely) but the impact on Hex has been considerable, with several members of the company including one of our leads being taken ill during the technical and preview period, and fresh bad news on that front again today."
London's Southwark Playhouse has closed its new musical The Rhythmics - described as Calendar Girls meets the Full Monty - three weeks early, after "disruption caused by ongoing illness and Covid-19 related absences in the company".
That was compounded by "the ongoing uncertainty in the wake of recent government announcements, leaving theatres once again facing a devastating loss of business", a statement from its producers said.
The Curious Incident of the Dog in the Night-Time at the Troubadour theatre in Wembley Park was forced to cancel its performances until Friday, while the capital's Donmar Warehouse has also been affected.
Performances of Force Majeure from Monday to Thursday were cancelled due to cases of Covid-19 in the company.
The theatre said in a statement: "We are very disappointed to have to cancel, but the safety of our performers, staff and audiences is our priority."
Rory Kinnear stars in the adaptation of Ruben Östlund's dark film comedy. Like many others, the play had already been rescheduled from 2020 due to the pandemic.
London's Bush Theatre also had to cancel a performance of critically-acclaimed Fair Play on Monday, but it is set to resume on Tuesday.
Moulin Rouge! at the Piccadilly Theatre in London restarted on Monday after a 10-day Covid-enforced break.
Some pantomimes have also been affected. The Brighton Centre's Aladdin, which was set to star Anita Dobson, has now been postponed until 2022 due to "the uncertainty and risk surrounding the Omicron variant of Covid-19".
The Chrysalis Theatre in Milton Keynes said it had taken the "very difficult decision" not to go ahead with its production of Peter Pan, after junior cast members caught the virus.
Steven Gordon-Wilson of 1702 Productions said the theatre space was shared with vulnerable groups, and the company felt cancellation was best.
Meanwhile, performances of Beauty and the Beast at Coventry's Belgrade Theatre have been suspended since 8 December and are not due to resume until 18 December at the earliest.
"Knowing this would always be a risk during the ongoing pandemic, we have taken the precaution of creating a professionally filmed version of our Beauty and the Beast production," the theatre said in a statement last week.
Jack and the Beanstalk from the Big Pembrokeshire Panto, which was due to star The Only Way is Essex's James Argent, has been cancelled too.
Rapunzel at the ADC Theatre in Cambridge has also been cut short, and the Byre Theatre in St Andrews, Scotland, has decided to lower the curtain on its version of Jack and the Beanstalk "in light of the current, rapidly evolving situation regarding the spread of the Omicron variant of Covid-19".
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