"And maybe we should have anxious most about COVID-19... not whether we have missing persons from a landslide", she said.
A landslide has smashed into a residential area near the Norwegian capital, injuring nine people and destroying several homes, authorities said.
"The 21 people may have evacuated themselves but may also still be in the landslide area", Pettersen told news agency NTB.
"What I saw were several houses that had collapsed, and some cars down there", Jenny Mikkelsen, a resident of Ask who lives next to the landslide, told Norwegian news outlet NRK.
Video footage from the scene showed a whole hillside had collapsed in Ask in the municipality of Gjerdrum, 25 kilometres (15 miles) northeast of the capital, leaving homes crushed and buried in dark mud.
According to police ten people had been injured with one being transferred to Oslo with serious injuries.
"We don't know if these people are in the landslide area, if they are away on holiday or in another way unable to contact police", the statement from police said.
At least 10 people are injured and a dozen are reported missing following a landslide in Norway.
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"There are many houses in the affected area", Roger Pettersen, head of the police operation, told reporters.
Nowegian rescue group Norsk Folkehjelp Follo said they had sent a total of 40 crew and 9 emergency ambulances to assist with search and rescue efforts.
"It hurts to see how the forces of nature have ravaged Gjerdrum".
Ask is home to 5,000 people.
Pettersen said it was not immediately known if there were any people missing and could not offer details of those injured. "My thoughts go to everyone affected by the landslide".
NRK said recent heavy precipitation may have made the soil unstable.
"This should have been a New Year's weekend where we should have had peace and quiet and maybe should have anxious most about COVID-19 and not whether we have missing persons from a landslide", Prime Minister Erna Solberg told broadcaster TV2.