A man armed with a bow and arrow killed five people and wounded two others in a series of attacks in the Norwegian town of Kongsberg, according to local police.
The suspect was in custody, police added.
"The man used a bow and arrow ... for some of the attacks," police chief Oeyvind Aas told reporters. The police were investigating whether other weapons had also been used, he said.
"The man has been apprehended ... from the information we now have, this person carried out these actions alone," Mr Aas added.
One of the wounded people was an off-duty police officer.
The motive for the attack, which took place in several locations in the town centre of Kongsberg, was not yet known, but police said terrorism could not yet be ruled out.
Newspaper VG showed images of an arrow that appeared to be stuck in the wall of a wood-paneled building.
The death toll was the worst of any attack in Norway since 2011, when far-right extremist Anders Behring Breivik killed 77 people, most of them teenagers at a youth camp.
The latest attacks took place over "a large area" of Kongsberg, a municipality of about 28,000 people in southeastern Norway, 68km from the capital, Oslo.
The government said police had launched a large investigation.
"The reports coming from Kongsberg tonight are horrifying," Prime Minister Erna Solberg told a news conference.
"I understand that many people are afraid, but it's important to emphasise that the police are now in control," she said.
Following the attacks, the police directorate said it had ordered officers nationwide to carry firearms. Norwegian police are normally unarmed but officers have access to guns and rifles when needed.
"This is an extra precaution. The police have no indication so far that there is a change in the national threat level," the directorate said in a statement.
Mr Aas said police would investigate whether the attack amounted to an act of terrorism.
Norway's minister of justice and public security, Monica Maeland, has received updates on the attacks and was closely monitoring the situation, the ministry said.
Norway has traditionally been a peaceful nation but has suffered far-right attacks.
In August 2019, self-proclaimed neo-Nazi Philip Manshaus opened fire into a mosque on the outskirts of Oslo before being overpowered by worshippers, with no one being seriously injured.
However, he had earlier shot dead his step-sister, who had been adopted from China, in what prosecutors termed a "racist act".
Several planned jihadist attacks have also been foiled by security services.