(Recasts with details on accident from Transportation Safety Board briefing)

By Mark Blinch

HALIFAX, Nova Scotia, March 29 (Reuters) - An Air Canada plane that suffered heavy damage in an accident in the east coast city of Halifax on Sunday landed short of the runway and hit an antenna array, losing its landing gear, safety officials said.

No one was killed in the accident that sent more than 20 passengers and crew to hospital. All but one of those treated had been released by later in the day, the airline said.

"They touched down 1,100 feet (335 meters) short of the runway, so I'd say they're pretty lucky," Mike Cunningham, an official with the Transportation Safety Board (TSB) of Canada, told a news conference.

He said when the plane landed short it hit an antenna array and "this caused considerable damage to the aircraft and the main landing gear came off at that point."

Cunningham, who noted one of the plane's engines had also detached, said it was too early to draw any conclusions about the accident. He also said it was too soon to rule out weather as factor.

The accident happened shortly after midnight. Air Canada said the Airbus A320 flying from Toronto was carrying 133 passengers and five crew members.

"We at Air Canada are greatly relieved that no one was critically injured. Yet we fully appreciate this has been a very unsettling experience," Air Canada Chief Operating Officer Klaus Goersch said in a statement.

Air Canada also said the weather was appropriate for a landing. It was snowing heavily at the airport at the time of the accident.

Passengers interviewed by local media described a "big flash" before landing and speculated the flight may have struck a power line.

Cunningham said he believed a power line had been severed near the airport, which lost power after that.

Photos posted online by the TSB showed the nose of the airline broken off and one wing badly damaged. (https://www.flickr.com/photos/tsbcanada/16342568434/)

Earlier this month, a Delta Air Lines Inc jet landing during a snowstorm at New York's LaGuardia Airport also slid off the runway and struck a fence.

(Writing by Jeffrey Hodgson; Editing by Gareth Jones and Eric Walsh)