The man who killed five people in a bow-and-arrow attack in Norway this week has been handed over to health services, the prosecution has said, amid speculation he may have mental health issues.

"He was handed over to health services on Thursday evening after an evaluation of his health condition," prosecutor Ann Iren Svane Mathiassen said.

Doubts have arisen about the mental health of the man identified as 37-year-old Danish citizen Espen Andersen Brathen, and whether he can be held legally responsible for the attack.

He has confessed to the killings.

A psychiatric evaluation began yesterday, which was expected to take up to several months.

Meanwhile, a judge was to decide later Friday whether to hold Mr Brathen in detention. The prosecution has asked for him to be held for four weeks, the first two in isolation.

If the judge grants the prosecution's request, he would not be jailed but rather held in medical care, the prosecutor said.

While police have said the attack was probably an act of terror, authorities have not ruled out the possibility of mental health problems.

"There is no doubt that the actual act appears as if it could be an act of terror, but it's important that the investigation continues and that we establish the motive of the suspect," the head of Norway's intelligence service PST, Hans Sverre Sjovold, told a news conference yesterday.

"This is a person who has been in and out of the health system for some time," Mr Sjovold said.

Norwegian authorities say the attack in the town of Kongsberg appears to have been an act of terrorism.

Emotions were still running high in Kongsberg, a quiet town in southeastern Norway, where residents gathered yesterday evening for a candlelit vigil 24 hours after the attack that left five dead and three injured.

"We're a small community and we need to be there for each other," Kristine Johansen, a 29-year-old teacher said.

The suspect was known to PST, which is in charge of Norway's anti-terrorism efforts, but few details have emerged about why.

"There were fears linked to radicalisation previously," police official Ole Bredrup Saeverud told reporters.

Those reports were before this year, and police had followed up at the time.

Norwegian media reported that Mr Brathen was subject to two prior court rulings, including a restraining order against him regarding two close family members after threatening to kill one of them, and a conviction for burglary and purchasing narcotics in 2012.

Local media also unearthed a video of him allegedly posted to social media in 2017, in which he issued a "warning" and declared his Muslim faith.

Mr Brathen is believed to have acted alone when he killed four women and a man, aged between 50 and 70, in several locations in Kongsberg where he lived.

The picturesque, tranquil town of 25,000 people is located about 80 kilometres (50 miles) west of Oslo.

Speaking anonymously, one of Mr Brathen's neighbours described the suspect as a big person with a crew cut and a serious demeanour, who was always seen "alone".

"No smile, nothing in the face. He was just staring," the neighbour said.

Norway rarely experiences such violence, but 10 years ago Anders Behring Breivik killed 77 people in the country's worst massacre since World War II.

Several planned jihadist attacks have been foiled by security services.