A tunnel expert says that whoever built the bunker recently discovered near a Pan Am Games facility in Toronto was lucky that it didn’t collapse in the process.

While the underground structure may look sophisticated, University of Toronto engineering professor John Harrison said it was poorly constructed and dangerous.

The bunker measures 1.9 metres tall by 0.9 metres wide, and is 10 metres long, police said. A three-metre-deep tunnel with a ladder leads into the bunker.

The walls were reinforced with wooden planks and moisture-resistant lights had been installed inside.

Harrison called it an "opportunistic design," telling CTV Toronto's Janice Golding it appeared that the builder or builders just used whatever materials they could scrounge.

"We can see that the plywood that was used to form the roof just simply wasn't being used properly. The vertical supports to the sides of the tunnel probably weren't supporting the sides of the tunnel to prevent it caving in," Harrison said Wednesday.

Based on photos of the bunker, it appears the walls could have caved in at any minute, he said.

"There's a lot about it that shows it to be amateurish and potentially dangerous."

He called the builders naive, saying they were lucky: "If it did collapse, they would not have been able to survive."

Police have not determined who built the bunker, but told media they suspect more than one person was involved.

If a single person built the bunker, Harrison estimated it could have taken more than two months to complete.

Deputy Police Chief Mark Saunders, who is the executive officer for Pan Am Games security, said no direct threats have been made against the games. A “robust security” plan is in place for the event, he told reporters on Tuesday.

Police are asking for the public’s help to aid their investigation. Anyone with information is asked to call 416-808-3100 or Crime Stoppers at 416-222-TIPS (8477).

With a report from CTV Toronto's Janice Golding