(Adds witness quotes)
LONDON, Dec 19 (Reuters) - Emergency services were called to London's Apollo Theatre on Thursday after people were injured by falling masonry, police said.
"We are aware of casualties," a police spokesman said.
A Reuters reporter at the scene said emergency vehicles had blocked off the street where the theatre is located.
A witness told Sky Television that part of a balcony in the auditorium appeared to have collapsed.
"I think the front part of the balcony fell down," Martin Bostock, who was in the audience, told Sky. "It was hard to see anything through the dust."
The Apollo is currently showing The Curious Incident of the Dog in the Night-Time.
(Reporting by William Schomberg; Editing by Kevin Liffey)