LONDON, Dec. 19 -- A total of 88 people were injured after the ceiling of a packed theater in downtown London collapsed Thursday, according to local authorities.

Seven of the wounded were in serious condition and were taken to hospital, said the London Ambulance Service in a statement.

The accident happened at the Apollo Theater where about 720 people were watching the popular play The Curious Incident of the Dog in the Night-Time when part of the theater's roof fell off.

The theater has a vertical design like a cylinder, with four levels and 775 seats. It was first opened in February 1901.

Hannah George and her husband from east London were among the audience sitting at the back of the balcony.

"It happened about 40 minutes after the show started," recalled the 29-year-old woman who said she was still "jittering" at the memory.

They heard crackling sound and saw clouds of dust at around 8:10 p.m. "I am not sure whether the creak and the fall were at the same time," she told Xinhua.

Like many others, she mistook the creak as part of the sound effect of the show at first, before seeing a "big crash" of the ceiling.

Spectators in the first row stood up and left the hall speedily, followed by those in the second and the third rows. "Most people got out very quickly," recalled George.

On their way out, the couple saw many were injured, mostly on their faces, heads as well as arms. Steve, the husband, remembered a man with bandage looking seriously injured, while Hannah noticed a woman on the floor receiving oxygen inhalation.

Eight fire engines with over 50 firemen as well as 25 ambulance workers and 12 officers rushed to the scene, according to local authorities.

Xinhua reporters saw a crane evacuating trapped audience and two stretchers hurrying off the site. One of the stretchers carried a person with a neck support, while the other carried one who was covered with a red blanket and had bandage around the head.

The Shaftesbury Avenue, where the theater is located, was closed and cordoned off. Police helped direct audience from other theaters in the street to leave.

Nick Harding, Kingsland Station manager, told the press that all the people trapped had been rescued within just a couple of hours.

"In my time as fire officer, I have never seen an incident like this," he said, "I imagine lots of people were out enjoying the show in the run-up to Christmas. My thoughts go out to all those affected."

Prime Minister David Cameron said in a twitter message that he had been updated regularly on the incident, and "grateful for the fast work of the emergency services in helping the injured."

A spokesman for London Mayor Boris Johnson said, "He has spoken to the Met Police Commissioner and is liaising with the relevant agencies. His thoughts and prayers are with those involved in what is clearly a very serious incident."