Lebanese security forces fired shots in the air and used water cannon in a vain attempt to prevent the crowd reaching the Danish Consulate.
Demonstrators threw stones at police, set several cars on fire, and rampaged through a Christian section of the city.
At least 18 people were reported injured in the disturbances.
The incident follows riots on 4 February in the Syrian capital, Damascus, in which the Danish and Norwegian embassies were set ablaze.
The Danish government has called on its nationals to leave Lebanon.
(Reuters, AFP, AP)