Fed up after the cries of his six-month-old son woke him up, a man struck the baby's head hard, causing multiple skull fractures.

Yesterday, the 30-year-old driver was sentenced to six years' jail and six strokes of the cane after pleading guilty the previous day to causing grievous hurt to his biological son, who now has permanent disabilities and has to be fed through a tube.

He cannot be named due to a gag order to protect the boy's identity.

The boy is currently two years and eight months old, but his developmental age is around four months. He cannot sit, move, turn or flip over on his own.

Before handing out the sentence, District Judge Eddy Tham said the boy had suffered "horrendous head injuries" and is now deprived of living an independent life.

The judge also said the man had breached the trust between a parent and a child.

The father of three was sleeping in his Bedok North flat when the boy's cries woke him up in the wee hours of Aug 26, 2016.

Deputy Public Prosecutor Grace Chua told Judge Tham: "The accused shouted 'Shut up lah, shut up lah. Later I have work, you make noise, I cannot sleep', and hit the victim once on the head with his right hand."

The baby began to cry even harder and vomited onto the floor before falling asleep.

He appeared normal when he woke up at around 8am but when his 26-year-old mother checked on him about five hours later, he was semi-conscious and weak.

An ambulance took him to KK Women's and Children's Hospital where a CT scan of his head revealed that he had multiple skull fractures.

He also had excess fluid in his brain and was immediately referred to neurosurgery. The court heard that he was discharged about seven months later on March 2 last year.

The boy is now living with his foster parents who are receiving financial aid from the Ministry of Social and Family Development, as well as the Assistive Technology Fund, a government-funded scheme administered by SG Enable.

DPP Chua said that to date, the boy has not recovered from his injuries. In June this year, his foster parents found that he was unable to move his limbs voluntarily. In terms of speech, the child only coos.

The DPP added: "It is important to continue early intervention and close medical follow-up to prevent further complications. However, the victim is likely to continue to require assistance in all activities of daily living and mobility."

The man is now out on bail of $15,000 and will surrender himself at the State Courts on Nov 23 to begin serving his sentence.