A tree collapsed on Northwestern University's campus Thursday during a winter storm, injuring four people, one of whom suffered serious injuries, authorities said.

Evanston police said the tree fell about noon and struck four pedestrians who were on a sidewalk at the campus just north of Chicago.

One person suffered serious injuries and was taken to Evanston Hospital with two others who had moderate injuries, said Matt Smith, a division chief with the Evanston Fire Department. He said the fourth person was treated at the scene.

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The tree fell as a winter storm was bringing snow and rain as well as strong winds to the Chicago area, Smith said.

"Snow, ice, wind combination contributed to the falling of a fairly large tree that resulted in injuries to the victims," he said.

Northwestern University officials told people to avoid the area around the Jacobs Center as emergency crews responded to the incident.