German police said Sunday a 21-year-old man who climbed onto the roof of the stadium during Germany's Euro 2024 clash against Denmark wanted to document the stunt.

The intruder at the Westfalen stadium in Dortmund told law enforcement after his arrest he only wanted to take "good photos", local police said in a statement.

The man was spotted in the rafters of the stadium on Saturday at 10:11 pm (2011 GMT) during the last-16 match, police said.

Authorities "observed the 21-year-old continuously", using police drones and a helicopter to illuminate the roof and track the situation, they said.

"At no point was there any danger to other people in the stadium," police said.

"The man finally followed the police's instructions and returned to a walkway under the roof at 11:44 pm," and was arrested.

Play in the match was interrupted in the first half due to intense thunderstorms around the stadium and rainwater pouring onto the pitch from the roof.

A search revealed the man on the roof was from Osnabrueck in northeast Germany and was "carrying camera equipment" in his backpack, police said.

Investigators have established that he has previously climbed other tall buildings in Germany on at least two occasions, they said.

According to German daily Bild, the man was following an online trend, in which people climb tall buildings unsecured and film themselves in the process to later post the images on social media.

Criminal proceedings had been opened against the climber on suspicion of trespassing, police said.

He was released from custody while the investigation continued.

Germany progressed to the quarter-finals of Euro 2024 with a 2-0 win against the Danes at the home of Borussia Dortmund.

Police said they would talk to tournament organisers UEFA about "how the accused was able to enter the stadium unhindered and get onto the roof".

"UEFA employs its own staff to ensure security in and around the stadium," police said.