Company cost-cutting could be to blame for a trench cave-in that trapped a Brisbane worker under two tonnes of earth for almost six hours, his union says.

Rescue workers said 31-year-old sub-contractor Mick Phillips, in agony for much of his ordeal, was lucky not to have been crushed to death.

Mr Phillips was relocating Telstra cables and conduits, as part of works for the Brisbane City Council, when the three-metre deep trench collapsed in Beatty Road, Archerfield, in Brisbane's south, about 1.30am (AEST).

Emergency crews undertook a meticulous six-hour rescue operation involving up to 25 workers, who used machinery before resorting to hand-digging and picks and shovels amid mounting fears of a further collapse.

Mr Phillips was eventually freed at 7.45am (AEST) and taken to the Princess Alexandra Hospital for treatment for injuries to a leg, which had been wedged between two telecommunication pipes.

Workplace, Health and Safety Queensland has launched an investigation into the incident.

A hospital spokeswoman said Mr Phillips was in a stable condition with no major injuries and remained under observation.

Mr Phillips, who was expected to stay in hospital overnight, released a statement thanking his rescuers.

"I'm glad to be out of the hole," he said.

"I'm very thankful to my work colleagues, to fire and rescue and to the ambulance guys."

Communications, Electrical and Plumbing Union (CEPU) telecommunications secretary Steve Mason called for a "full and thorough" probe into the trench cave-in.

"He was an ex-Telstra employee ... (Telstra) don't have enough people working in the telecommunications industry because of their downsizing program - this has forced a lot of ex-Telstra employees to become sub-contractors (with contract companies)," Mr Mason said.

"It's all about Telstra making the best profit for shareholders - instead of them employing full-time employees they contract out the work, where corners may be cut at the expense of workplace, health and safety."

But operations and maintenance provider Transfield, which was carrying out the works, brushed aside CEPU allegations that Mr Phillips could have been put in harm's way because of cost cutting, saying the company had stringent safety regulations.

"We view any incident at work as serious and we investigate immediately - we are very, very proud of our safety record," a Transfield spokesman said.

"We are not interested in engaging in a political debate with anyone - our concern is for the injured contractor and his welfare."

A Telstra spokesman said: "It's opportunistic in that the union are seeking to use today's incident as an opportunity to criticise Telstra in broader terms."

"The point the union want you to overlook is that in terms of today's incident, Transfield is contacting for Brisbane City Council not Telstra."

Queensland Fire and Rescue Service special operations acting manager Gary Littlewood said Mr Phillips had been "in a lot of pain" with paramedics administering medication to keep him calm and prevent him going into shock.

"They were digging a trench and two of the guys were walking with a length of pipe along the edge of the trench when a big slice of it fell off into the trench," Mr Littlewood said.