The Serious Fraud Office has executed search warrants at multiple properties in its probe of people linked to Auckland Transport.
The SFO confirmed today it had launched an investigation into people related to the council body and has "reasonable grounds to believe that an offence involving serious or complex fraud may have been committed".
Its investigation involved alleged "irregularities in the procurement of services" and the SFO said search warrants were executed yesterday.
The matter had referred to the SFO by Auckland Transport and acting SFO chief executive Simon McArley said no further comment would be made.
The fraud watchdog's involvement follows Auckland Transport sacking a senior manager last month during an investigation of roading contracts and alleged corruption.
At that time, the SFO was only keeping a watching brief on the matter rather than the formal probe it has since launched.
An Auckland Transport spokesman said its own investigation had concluded and the probe was now being handled entirely by the SFO.
The spokesman said he couldn't comment when asked if any more staff at the council body had been sacked as part of the corruption probe.