LONDON — A gunman opened fire in a Muslim prayer center in Zurich, the largest city in Switzerland, late on Monday afternoon, wounding at least three people, according to the police.

Around 5:30 p.m., the gunman entered the prayer center, in a neighborhood known as Aussersihl, just south of the city’s main train station. Several worshipers were praying. The assailant opened fire, injuring three men, ages 30, 35 and 56, before fleeing. The men were taken to a hospital. Two of the three were injured seriously, and one was lightly wounded, the police said.

The police said the gunman was about 30 years old and was wearing dark clothes, including a dark woolen cap.

Police officers from both the city and the canton of Zurich sealed off the area, a police spokeswoman, Judith Hödl, said in a statement. “At the moment, no further information can be provided on the affected parties and on the crime,” she said, adding an appeal for witnesses to come forward.