WorkSafe is investigating the fatalities, the first of which occurred on July 18 in Wairarapa.
It was followed by the death of Canterbury farmer Neil Evans after a crash on his Omihi farm, near Amberley, on July 22, then in Southland on July 26 and Northland on July 30.
All of the incidents coincided with the start of lambing and calving season.
And on July 15, two people in the Tasman District were also injured after a quad bike rolled on a farm in Mahana.
WorkSafe principal inspector Graham Bates said their sympathy was with every family and community mourning the sudden deaths.
"Although our investigations are in their early stages, the trend is worrying enough for us to sound the alarm already.
"Sloped surfaces and steep terrain can be especially problematic and have, sadly, been a factor in some of the recent cases."
Bates said a risk assessment of terrain and tasks must be the top priority for farm workers before getting on a quad bike - especially at this time of year.
"Farm vehicle incidents are one of the top two causes of workplace deaths in Aotearoa, which is why agriculture is a priority sector under WorkSafe's new strategy.
"We are targeting the biggest risks and working with the sector to improve health and safety in agriculture."
WorkSafe messages to reduce harm on farm
- Install a crush or rollover protection device on quad bikes
- Choose the right vehicle for the job and ensure that the driver is competent
- Always use a seatbelt and helmet
- Consider quad bike training
- Prioritise maintenance, including attachments, tyres and brakes
- Remember tired people make mistakes
- Ensure the vehicle is safely stopped and brakes engaged before getting off
- Seek help when needed - neighbouring farmers are always more than willing to lend a hand.
