Rikki the Belgian Malinois paws at his muzzle as his handler surveys the thousands of German and Polish fans partying on the steps outside Cologne's spectacular cathedral.

Bottles crash and chants reverberate against the cathedral's walls but the mood is far from dark. Not even a sudden downpour and the crackle of lightning can dampen the revellers' spirits.

Rikki's muzzle will stay on tonight.

"If there's trouble, I go in with the dogs," the chief handler on patrol told Reuters outside the city's main train station, hours after Germany's last-gasp win over Poland.

"If they don't disperse, the muzzles come off and we clean up."

Most German police forces have switched to the Malinois from other breeds such as the German Shepherd due to its agility and high "prey drive".

The breed is described on websites as a "no-nonsense dog, unmatched in terms of toughness and focus."

"The Malinois is more agile than the German Shepherd, which has a lot of problems with its hips," said another handler as he pulled hard on the choke chain to restrain his dog.

"This one is only three and just out of training, it's better if we keep him apart from the others."

Rikki and the other members of the K-9 unit have seen little action since the World Cup kicked off on June 9, but the handler said that did not concern them.

"They are not overly aggressive dogs," he said. "They live at home with us and our families."