The family of a farmer who was shot and killed at his home in Cullinan on Monday says criminals are after farm land in the area.

Henry Locke was shot dead in front of his two children and wife when three gunmen broke into his home in the early hours of Monday morning.

Locke's sister-in-law, Estelle Maritz, says farmers in northern Gauteng are under attack.

Maritz says her sister went outside to see why the dogs were barking just after midnight on Sunday when three robbers barged into their home and held them at gunpoint.

She says they tried to grab her 13-year-old niece who ran into her parent's bedroom to alert her father.

Maritz says the robbers shot Locke before he even managed to comprehend what was going on.

"They shot him right in the heart and he died immediately."

She says this is not the first time that farms in the area have been targeted.

"It is getting terrible on the farms. I think they want our land and they are not going to make a success of it after all."

The gunmen made off with two cell phones and a laptop.