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 on Wednesday, local police said.

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," Aas added.

One of the wounded people was an off-duty police officer.

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 attacks on Wednesday took place over "a large area" of Kongsberg, a municipality of about 28,000 people in southeastern Norway, 68 km (42 miles) 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.

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.