Ontario's Ministry of Labour has issued three orders, including not to disturb the scene, after part of a tunnel wall collapsed at an Ottawa light rail construction site Thursday afternoon — stranding three workers underground.

Emergency crews were called to Laurier Avenue and Waller Street just before 4:30 p.m. to rescue three workers from the tunnel.

The Rideau Transit Group, the consortium building Ottawa's $2-billion light rail line, said workers were applying shotcrete — a sprayable concrete used to reinforce structures — when a steel cage designed to provide stability came loose from the tunnel wall.

One worker had to be taken to hospital with a hand injury, while two others were unhurt.

It's the third incident at an LRT construction site this year that has prompted a Ministry of Labour investigation.

A ministry investigator was in the tunnel Friday gathering information and evidence. An employee at the site said all work had stopped while the investigation is underway.

The latest incident at Laurier and Waller has prompted the ministry to order:

That the scene is not to be disturbed.

Rideau Transit Group to provide (unspecified) documentation.

Hard Rock Concrete, a secondary employer, to provide (unspecified) documentation.

The City of Ottawa said no one was available for an interview on Friday but issued a short statement.

"RTG is currently working with the Ministry of Labour. Work is expected to resume as soon as possible."

Emergency vehicles rushed to the scene of the industrial incident in the LRT tunnel near the University of Ottawa. (Jacques Corriveau/CBC)

Union has concerns about worker safety

Sean McKenny, the president of the Ottawa and District Labour Council, said he was concerned and frustrated with the lack of information about the injuries involving at least one worker at the site.

McKenny fears the incident will only add to delays, and since the employer is responsible for paying costs associated with delays, there will be pressure on workers to meet deadlines.

"There is an expectation within the construction sector that when you push, it results in much more frequent accidents," he said.

"They're pushed, corners are cut, all in the name of getting the project in on time."