Prosecutors will apply to have Oscar Pistorius committed for one month of mental evaluations after a psychiatrist on Monday told his murder trial the Paralympian suffered from an "anxiety disorder".

>> Witness feared Pistorius might shoot himself

Prosecutor Gerrie Nel argued the sprinter should go to a facility for 30 days to test a defence psychiatrist's claim that the condition may have had an impact on his state of mind before he shot and killed his girlfriend, allegedly believing she was an intruder.

"Then I'll bring the application," he said, after a heated to-and-fro with defence lawyer Barry Roux and defence witness Meryll Vorster.

Opening the eighth and perhaps final week of evidence, Roux called the forensic psychiatrist to testify about the 27-year-old's feelings of vulnerability.

"It is my opinion, my lady, that Mr Pistorius has an anxiety disorder," said Vorster, recounting stressful factors in the Paralympic gold medallist's life.

"If he was afraid that there was an intruder, then certainly having a generalised anxiety disorder would have affected the way he reacted to that fear," she added.

The court adjourned early for the prosecution to study the psychiatric report, before more questioning on Tuesday and the formal application for tests.

During two months of trial, the defence has sought to portray the world-famous athlete as almost manically obsessed with safety after a difficult childhood and in the face of high crime levels in South Africa.

The star sprinter claims he mistakenly shot girlfriend Reeva Steenkamp through a locked toilet door, believing she was an intruder in his upmarket Pretoria home.

'Threatening environment'

Pistorius, nicknamed the "Blade Runner" for his prosthetic limbs, has pleaded not guilty to intentionally killing Steenkamp, as well as three other firearms charges.

If found guilty of premeditated murder, Pistorius faces 25 years in South Africa's notoriously brutal jails and an abrupt end to his once glittering sporting career.

Vorster, who also interviewed Pistorius's close family and friends to compile her report, said the athlete's disorder began when his parents encouraged the double-amputee to be normal.

"Over time this could result in anxiety," she said.

The Pistorius children were not "soothed" by their mother, Sheila, who slept with a firearm under her pillow and "abused alcohol intermittently," continued the psychiatrist.

"The children were reared to see their external environment as threatening," said Vorster, who said Pistorius's mother "added" to her children's anxiety.

As the psychiatrist was giving her testimony, Pistorius appeared to become emotional, his face turning red. His sister Aimee sat stone-still, staring into the distance.

When Pistorius's mother died when he was a teen, the star sprinter lost his only adult role model, said the psychiatrist. His parents were divorced at the time.

At age 21, a rising athletic star and financially independent Pistorius "broke all ties with his father," she said. Soon after, he bought a gun.

"Individuals with an anxiety disorder work hard to control their environment," said Vorster, wearing black-framed glasses and a black blazer, "in a way, his strict training regime and his diet helped him to alleviate his levels of anxiety."