A tweet from the cinema's official Twitter account read: "Another @riocinema first!
"Still 5 days to Valentines Day but @idriselba went down on one knee and proposed to his girlfriend live on stage this morning before a preview of his film #Yardie."
A spokesman added: "She said yes and there was much clapping and cheering."
A video shot by audience member David Marsden-Sainou from inside the cinema showed Elba, 45, down on one knee before the couple embraced to applause.
Other Twitter users confirmed they witnessed the happy event.
One posted: "At cast & crew screening of @YARDIES & @IdrisElba just proposed to his girlfriend Sabrina!! Too cute."
When you turn up to watch the #Yardie screening with @Sainou clients @adnanmust_ & @AkinGazi and the director @idriselba steals the show... #marriagepropsal pic.twitter.com/aLYsnMNbzA— David Marsden-Sainou (@AgentMarsden) February 10, 2018
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