The ceiling of a London theater partially collapsed Thursday night, showering a packed audience with heaps of plaster, wood and dust. More than 80 people were injured _ at least seven seriously _ and several trapped theater-goers had to be rescued, authorities said.

The collapse at the Apollo Theatre took place at 8:15 p.m. during a performance of “The Curious Incident Of The Dog In The Night-Time” at the height of the Christmas holiday season.  Plaster from a section of the ceiling tumbled down, bringing parts of the theater's balconies with it, police said.

Over 700 people were in the theater at the time, according to the London Fire Department.

Brian Reardon, a fire brigade commander on the scene, said he did not believe a lightning strike caused the ceiling to collapse but added that the cause would not be known until a full investigation was carried out. London was hit by an extremely heavy thunderstorm about 7 p.m., an hour before the collapse.

“Complete chaos” erupted as the debris rained down, said Martin Bostock, who came with his family to see the show, which is based on the best-selling novel by Mark Haddon.

“At first, we thought it was part of the show,” he told Sky News. “Then I got hit on the head.”

Scott Daniels, an American tourist who lives in the Dallas area, was in the audience, too. He said he started hearing noises and screaming, before “huge hunks of plaster” started raining down.

“I thought, well, maybe this is part of the play,” he told The Associated Press. “A lot of action and dialogue was happening at the same time on stage, but then when the lights went out and everything filled with dust _ everybody was coughing and choking.”

Dust-covered theatergoers, many with bandaged heads, were treated by dozens of emergency workers in the street outside the Apollo and at a nearby theater.

London's Ambulance Service said it treated 88 patients _ 81 with minor injuries and seven with “more serious” injuries who were taken to nearby hospitals. None of the injuries were believed to be life-threatening, officials said.

A London city bus was commandeered to take some of the wounded to the hospital.

The fire department reported that all those who had been trapped in the Apollo have been rescued.

Shaftesbury Avenue, normally one of London's busiest streets and teeming with pedestrians, was completely shut down by emergency workers.

The Apollo Theatre, named for the Greek and Roman god of music and the arts, was built in 1901 and has 775 seats.

The show, which is aimed at young people as well as adults, is about a boy with Asperger's who sets out to solve a crime.

Prime Minister David Cameron said via Twitter that he was being updated regularly on the crisis. He praised the city's emergency services _ who were on the scene within three minutes _ for their “fast work” in helping the injured. (AP)