Four workers have been taken to hospital following an explosion at a Melbourne CBD construction site.

Emergency services were called to the eastern end of Bourke Street, near Parliament, about 8.50am on Thursday.

“It is believed the pump line of a concrete truck blew out, injuring four workers,” a Victoria Police spokesperson said.

The workers were seen being stretchered into ambulances, one with a bloodied face.

Harry Young works at a nearby shop and had just started the day when he heard a loud bang.

Mr Young said he did not think much of the noise, as work has been underway at the loud construction site for about a year.

But he did say it sounded “abnormal” and “out of the ordinary”.

“Next thing you know, there’s fire engine, another fire engine, police car, ambulance,” he said.

Mr Young said one of the tradies ran out dazed onto the street “looking very distressed” and shouted an expletive.

“You wouldn’t wish that on your worst enemy, to have a problem like that at work,” Mr Young said.

“Especially here.

“It’s horrendous, it’s dangerous as hell.”

Ambulance Victoria said paramedics treated four people at the scene.

Two men – one believed to be in his 30s and another in his 20s – were taken to the Royal Melbourne Hospital in stable conditions after being treated for upper body injuries.

The other two men, both believed to be aged in their 30s, were taken to The Alfred hospital in stable conditions after being treated for upper body injuries.

Traffic was cut off around the work site and a large emergency services presence was at the scene.

WorkSafe Victoria has been notified, and a spokeswoman said the agency was making inquiries about the incident.