The man suspected of shooting at people inside a Norwegian mosque on Saturday and of killing his Chinese-born stepsister, appeared in court on Monday with black eyes and wounds on his face and neck.

A judge gave police permission to hold 21-year-old Philip Manshaus (photo, above) in custody for an initial four weeks while he is investigated on suspicion of murder and breach of anti-terrorism law, the court's ruling later showed.

Manshaus, who briefly smiled at photographers, does not admit to any crime, his lawyer said.

Witnesses said Manshaus entered the al-Noor Islamic Centre with several guns, but was overpowered by a 65-year-old member of the mosque, who managed to wrestle away his weapons in the fight that followed.

Manshaus wore a helmet camera to film the shooting but did not appear to have broadcast the attack, according to prosecutors.

"This video is key evidence," police attorney Paal-Fredrik Hjort Kraby told a news conference.

Manshaus, whose home is near the mosque just outside the Norwegian capital, had expressed far-right, anti-immigrant views before the attack, police said.

Online postings under Manshaus' name, made shortly before the attack, expressed admiration for the massacre of more than 50 people at two New Zealand mosques in March by a suspected white supremacist, who filmed and broadcast the killings live online.

Reuters could not independently verify that the postings were made by Manshaus.

A few hours after the Norwegian mosque attack, police discovered the body of a young woman at what they said was the suspect's address. Police later named her as his stepsister, Chinese-born Johanne Zhangjia Ihle-Hansen.

The 17-year-old was adopted as a small child by a Norwegian woman, who is now the spouse of Philip Manshaus' father, the mother's lawyer said.

"These hours after what happened have been chaotic, unreal, a tragedy," the lawyer, Elisabeth Hagen, told Reuters.

"These are two tragedies, one with the girl and one with the mosque. I represent the mother of the girl," she said, adding that the girl's mother and Manshaus' father were together and surrounded by friends helping them cope.

Hagen declined to comment on any possible motive for the killing.

Manshaus did not speak while reporters were present and has so far declined to talk to the police.

"He is exercising his right not to be interrogated," his defence attorney, Unni Fries, told Reuters. "He is not admitting any guilt."

Police sought to hold him on suspicion of murder, as well as of breaching anti-terrorism law by spreading severe fear among the population when firing several guns at the mosque.

While some of the weapons had been legally obtained by one or more residents at Manshaus' home, others may have been illegal, police said.

The Norwegian police security service, PST, which monitors and investigates extremist threats, said on Monday it had received a tip-off regarding Manshaus last year but had not launched an investigation at the time.

"There was nothing in that tip-off that suggested there was danger of an act of terrorism or that planning of an attack was underway," PST head Hans Sverre Sjoevold told a news conference.

He declined to comment on the content and source of the warning.

PST will now explore whether Manshaus had links to any domestic or foreign extremist networks, although investigators have said they believed he acted alone in the attack, Sjoevold told Reuters.

In 2011, anti-Muslim neo-Nazi Anders Behring Breivik massacred 77 people in Norway's worst peacetime atrocity, the majority of them teenagers at a youth camp.

Norwegian Prime Minister Erna Solberg on Sunday said that while her government was trying to combat hate speech, more must be done.

"We are trying to combat this, but it's a challenge. I think it's a word-wide challenge in a sense," Solberg said.

Any formal charges in the case, and a trial to decide whether Manshaus is guilty or not, are likely to still be months away.

A guilty verdict on charges of breaching anti-terrorism laws can carry a sentence of up to 21 years in prison, as can the killing of the suspect's 17-year-old stepsister, according to Norwegian sentencing guidelines.

- Reuters