The alarm came shortly after 10 a.m. on Saturday. According to police, the activists got in by climbing over a fence.
"It's an ongoing operation. The police are trying to get them to leave voluntarily," police spokesperson Susanna Rinaldo said an hour later.
The climate activists say they are staging actions outside the airport and inside a private jet terminal. Their aim is to stop private flights.
A person is glued to the nose wheel of an airplane, says Rinaldo.
The police do not want to say how many people are involved.
According to Swedavia's website, there are no scheduled flights to or from Bromma on Saturday.
"We can confirm that the police are on site and handling a situation. Regular traffic is not affected by this," says Susanne Norman, Swedavia's chief operating officer, in a written statement to TT.
Shortly before noon, the police announced that five people had been arrested on suspicion of airport sabotage. Four people had been reported for violating the Protection Act, and ten for disobeying the authorities. The police operation is still ongoing.
