Danish police on Tuesday said it had arrested a man suspected of seriously wounding one of its officers by shooting him in the head outside a police station in a Copenhagen suburb earlier in the day.

Police said the 26-year-old suspect was known to the force and that it believed he had acted alone. He was detained in Albertslund, where the shooting occurred.

The officer's condition was deemed serious by medical personnel, but not critical, police said at a briefing.

Police stations across Denmark were put on alert and heavily armed officers were deployed around stations in Copenhagen, but these measures were reversed after the arrest.

"After the arrest of the alleged shooter, all extraordinary security measures at our stations have now been called off," Danish police said on Twitter.

The shooter will appear in court on Wednesday for preliminary questioning related to charges of assault with intent to kill.