Police later confirmed that the alleged perpetrator has been arrested.
The incident took place in Nore, in the Numedal valley near the capital, Oslo.
Norwegian broadcaster TV2 said that there were several ambulances, including air ambulances, at the site, plus numerous police vehicles.
William Scott told the VG newspaper he saw an injured woman lying on the ground after the attack.
“At first I thought it was a collision because there was a large pool of blood on the ground,” he said.
Nore is close to Kongsberg, where five people were fatally stabbed and four wounded last October when Espen Andersen Brathen attacked strangers with a bow and arrows and knives.
He has pleaded guilty in a trial that started this week.
Brathen also faces 11 counts of attempted murder for the attack in Kongsberg, a former mining town of 26,000 people.