Neighbours overheard the attack and rushed to help the couple, who were taken to Tokoroa Hospital by ambulance.
Police used a dog to track the offenders but lost the trail some distance from the scene.
The men were described as Maori, aged between 18 and 20 years.
Two of the men were described as being overweight, and all were wearing dark clothing.
Tokoroa Police Senior Sergeant Graeme Hill said: "This is a cowardly and despicable attack on two elderly people minding their own business at home. I urge anyone with any information that can assist in the apprehension of these offenders to contact us."
Anyone with information is asked to contact Tokoroa Police on (07) 885 0100 or call Crimestoppers anonymously on 0800 555111.