Police, who rushed to the scene in a central neighbourhood known for trendy cafes and the city's red-light district, were also investigating a possible connection to the discovery of a corpse at nearby Gessner bridge over the Sihl River, police spokesman Marco Bisa said yesterday.
Authorities weren't considering the attack as terrorism, he said. Police also said it was too early to determine whether there might be any link to an incident in Berlin also on yesterday, where a truck rammed into a Christmas market, killing at least nine people.
Bisa said the injured were hospitalised and were aged 30, 35 and 56 years old, but did not specify their nationalities. He said witnesses described the attacker as clad head to foot in black, and was believed to be aged about 30 years old.
At the scene, Abukav Abshirow, a 30-year-old Somali man who works at a Zurich car dealership, said his friend was among the injured. He recalled how they had been celebrating a religious occasion at the centre the night before.
Attacks by gunmen are rare in Switzerland. The country was shaken in 2013 by at least two multiple-fatality shootings. The country has a long-standing tradition for men to keep their military rifles after completing compulsory military service which partly explains a high rate of gun ownership in the country of about 8.2 million people.