Thursday's American League baseball game between the Toronto Blue Jays and Kansas City Royals was called off after the retractable roof at SkyDome jammed during a test run, sending chunks of the roof crashing to the field below.

"Some very big pieces of metal fell on to the field," Blue Jays president Paul Godfrey said. "We're very, very thankful there was no one on the field that could have got hurt."

The biggest piece that came down was estimated at eight feet by six feet (2.4 metres by 1.8 metres).

A hole in the roof was plain to see from outside, with some debris hanging out.

Insect-like engineers, tethered by wires, checked out the damage on the outside of the white roof high above the city's waterfront as commuters raced home on a nearby expressway.

The contest was originally slated to start at 7:05 p.m. EDT.

Jays officials pushed back the start time to 8:05 p.m. EDT, but eventually called it off at around 6:15 p.m.

The gates never opened so fans did not get into the building.

"I think everybody feels more comfortable with that decision," said Godfrey, citing the safety of fans and players.

There were some 10 smaller sections of the roof that were loose and needed to be secured.

That was expected to take about 10 hours.

"We don't know the extent of the damage," Godfrey said.

Royals pitcher Doug Henry was in the dugout when one of the large metal pieces fell.

He was adamant about calling off the contest.

"There's no way we should play," Henry said. "You've got stuff falling down.

"They have to have inspectors and check it all. The piece that just fell is at least 10 feet long.

"It had to weigh a couple of hundred pounds. You don't want it coming down on the field or on the fans.

"There's no way we should play."

The damage occurred during a routine test opening at 3 p.m. Thursday.

A giant panel -- one of three moveable panels in the roof -- jammed, causing another panel to ram into the stalled section.

That ripped off some sheet metal and insulation which fell to the ground below in left field.

The field was cleared and no one was hurt.

There were a couple of Kansas City players out at the time, playing catch. Batting practice usually start at 4 p.m.

The debris was removed from the field and the roof closed.

TSN, which was scheduled to show the game, showed footage of the pieces of aluminum siding and insulation falling in the afternoon.

SkyDome opened in 1989 at the cost of more than $500 million.

When the roof opens, Panels 2 and 3 slide on parallel rails while Panel 1 slides on a circular rail, tucking under the other two.

Panel 3 stopped moving and was hit by Panel 1 when it swung around.

"You've got 11,000 tons of roof up there moving, and even when you're closing it or opening it slowly, there's a lot of momentum, and if those control systems fail, you're going to have a little bit of a problem," said Norman Seagram, the president of Sportsco, which owns SkyDome.

"Some of the controls that are supposed to prevent this kind of accident didn't work for some reason."

There was no immediate word on when the game might be made up.

The two teams are next scheduled to play again Friday at 4 p.m. EDT.

The domed stadium has had a checkered history, which has featured lawsuits from a fan being hit with a baseball to battles over catering rights.

In 1996, a man died after falling while practising for a rappelling exhibition scheduled for the next day at a Toronto Argonauts football game.

William Muller fell some 36 metres.

In 1998, former Toronto outfielder Rob Ducey received a reported $700,000 out-of-court settlement with SkyDome and the Blue Jays.

Ducey, a native of Cambridge, Ont., had claimed in a lawsuit his baseball career had been derailed after injuring his knee in 1989 when he ran through a dislodged piece of fence and landed on concrete.

SkyDome is still home to the Blue Jays and CFL Argonauts.

It also hosts concerts and conventions, from Billy Joel to monster trucks.

Once labelled one of the wonders of the world, with its roof, built-in hotel and giant Jumbotron screen, it has been surpassed by newer, even fancier stadiums since.

By Pierre LeBrun