"The serious crash unit is investigating and one avenue is that the crash was possibly caused by sunstrike," he said.
The injured man has been transferred to Waikato Hospital for surgery. Rotorua Contracting is a business unit of the Rotorua Lakes Council.
The council was providing support for the man and his family as well as his colleagues, said Rotorua Contracting chief executive Tim Hammond.
It is also conducting an internal investigation, alongside investigations by police and WorkSafe.
"This is obviously traumatic for everyone who is directly involved," Mr Hammond said.