Pieter Doorewaard, 28, and Philip Schutte, 35, were found to have killed 15-year-old Matlhomola Mosweu, also spelt Moshoeu, on April 20, 2017, after claiming they caught him taking a plant from a farm in the area.

Doorewaard was jailed for at least 18 years and Schutte was jailed for at least 23.

The boy died after being thrown out of a moving vehicle driven by the pair and suffering a broken neck, in a case that sparked rioting and looting of white-owned businesses in the town of Coligny.

The men had claimed that the teen jumped off the truck as they drove him to the police but it was Schutte who was found to have thrown the boy to his death.

Judge Ronald Hendricks previously also found the pair guilty of kidnapping and intimidation.

"Murder is undoubtedly the most serious offence that can be committed," Hendricks said.

"You picked up the deceased and threw him from the van onto the ground.

"Your actions that day... were indeed disgraceful."

Ahead of the sentencing, Schutte's wife adjusted his collar and kissed him in the dock.

The judge paused as his comments were translated into Afrikaans, the language spoken by many white farmers in South Africa.

"It cannot be ignored that the community revolted as a result of this incident," the judge added.

'Inaction of the police'

"This was largely because of the inaction of the police," Hendricks said. "The community of Coligny was polarised as a result of this incident."

Other family members looked on as the judge announced his ruling -- as did members of the radical Economic Freedom Fighters Party, which has vigorously opposed racism against the country's black majority.

Mosweu's father Sakie Dingake said he "was hoping for a sentence of more than 30 years and it did not happen".

"It's so hurtful to me because my child is gone, he is not coming back. These people are going to jail but there is a possibility that if they behave, they can get parole and come out," he said.

A community leader speaking in court said: "It's not all whites in Coligny who are racist -- it's a pocket."

"(Society) has to operate like a piano -- you play black and white keys together you get a melody," he added.

Racially charged incidents between white farm owners and managers and poor black farmhands are common in South Africa.

In 2016 two white farmers in eastern Mpumalanga province forced into a coffin a black man they accused of trespassing.

'Too young to die'

The case sparked outrage after a video of the incident emerged on social media and the two were handed jail terms of 19 and 16 years.

Judge Hendricks said in mitigation of Doorewaard and Schutte's sentences that "there was no direct intention to kill the deceased".

"(You are) first-time offenders," he added, as another reason for not imposing life sentences.

"However the aggravating circumstances of this case far outweigh mitigating (factors)."

Local pastor Tewie Pieters said the pair would appeal the sentence with support from the Afrikaans rights group AfriForum.

The government said in a statement that "South Africans should not allow actions like that of the two men to divide our country and communities".

"Government calls on all parties to work together to foster reconciliation," it said.

Beth Sifuba, Mosweu's grandmother, said the sentences were "too little".

"When they come out their kids will be there waiting for them. Where will our child be?" she said. "That child was too young to die."