A St John spokesperson said they were called to an incident on South Rd in Hawera yesterday afternoon.
"Two rapid response units and one ambulance responded to the scene and treated, then transported one patient in a serious condition to Taranaki Base Hospital."
A McDonald's spokesperson said there was an incident at their Hawera branch between members of the public on Monday.
"We are assisting police with their investigation, including providing CCTV.
"Staff present at the time of the incident are being supported, and have been offered our employee assistance programme."
Information can be provided by contacting Police on 105 or online.
Information can also be provided anonymously via Crime Stoppers on 0800 555 111 or www.crimestoppers-nz.org.