Investigators are probing whether the vehicle may have crashed into the scaffolding before it fell.

JOHANNESBURG - Murray & Roberts says it's looking into claims that a cement truck may have crashed into the bridge before it fell after initially saying that strong winds were to blame for the collapse.

The construction giant says the cement construction truck doesn't belong to the company.

Investigators are probing whether the vehicle may have crashed into the scaffolding before it fell.

The truck's window screen was shattered when a piece of scaffolding fell on it.

Construction workers are working as quickly as possible to clear and reopen the M1 highway before the afternoon traffic rush in Sandton.

A motorist says the roads were chaotic this morning.

"My legs are so sore, I even had cramps. People are diverting, some are lost, and they don't even know how they are going to come out of this place."

Most of the scaffolding has now been removed but it's unclear when authorities will reopen the highway. WATCH: Pedestrian bridge collapse kills 2 on M1

'WORST TRAGEDY'

Murray & Roberts described the collapse as one of the worst tragedies.

CEO Henry Laas has vowed to do everything possible to prevent this from happening again.

"The erection took place under the supervision of qualified engineers, so we really don't understand what led to this."

Laas says he could not get any rest last night following the accident and has sent his condolences to the affected families.

Three quarters of the collapsed scaffolding is still obstructing both sides of the highway .

Workers are using heavy machinery to remove the collapsed structure.

This is being done carefully, but the race is on to open the highway and allow traffic to flow.