Investigations into the collapse the bridge linking Sandton and Alexandra township have been announced by various agencies as the Minister of Transport called for an investigation on Thursday.

Construction company Murray & Roberts launched a formal investigation into the collapse of the bridge over the M1 highway on Wednesday‚ the company said on Thursday.

Investigations have also been initiated by the Department of Labour‚ the City of Johannesburg‚ the SAPS‚ and other parties‚ with which Murray & Roberts is cooperating.

The investigations will include analysis and research conducted by technical‚ engineering‚ legal and forensic specialists‚ the company said in a statement.

Emergency services officials said three people were killed in the incident‚ while 19 were injured.

The collapsed structure was part of a walk-way bridge constructed for the estimated 10 000 pedestrians who cross the Grayston off ramp from Alexandra to Sandton and vice versa daily.

Transport Minister Dipuo Peters says there is a need to unearth the reasons behind the tragic incident in order to prevent a recurrence in the future.

Peters says the bridge was an important aspect of the overall development of economic infrastructure currently underway to improve access to Sandton.

"Sandton is a critical economic hub not only for South Africa‚ but the continent and the world at large. It's for this reason it's called ‘the richest square mile in Africa’. Seamless accessibility into Sandton is critical for both motorists and pedestrians‚ hence the need for such infrastructure‚" said Peters.

Murray & Roberts spokesman Eduard Jardim said independent investigators had been appointed‚ but finding the cause of the collapse could take weeks‚ if not months.

“We would caution against speculation as the causes for this tragic event need to be thoroughly and properly investigated‚” the company said.

The mangled structure sprawled across Johannesburg's M1 highway near a busy offramp leading to the Sandton financial district‚ caused hours of delays for motorists during evening peak traffic on Wednesday and again on Thursday morning.

Meanwhile‚ the Gauteng Department of Health conveyed its condolences to the families of those who lost their lives and hoped for a speedy recovery for those injured in the incident.

The department also released information regarding the hospitalisation of those injured. It said:

- Charlotte Maxeke Academic Hospital had admitted three patients who are in a serious but stable condition at the trauma ICU;

- Tembisa Hospital admitted nine patients. Of those‚ seven were admitted with serious injuries‚ while two were assessed and discharged yesterday; and

- Helen Joseph Hospital treated two patients‚ who were both discharged on Wednesday.

MEC for Health in Gauteng Qedani Mahlangu said: “We would like to thank Emergency Medical Services‚ officials from both private and public sectors‚ nurses‚ doctors and other officials who worked tireless to save lives‚ their diligent work will always be appreciated.”