(CBS) — Chicago police did a sweep of a mostly empty Wrigley Field on Sunday night to investigate a bomb threat that was phoned in but which turned out to be unfounded.

Sports journalists on the scene said police and K-9 units were in and around the North Side ballpark around 6 p.m. Wrigley was evacuated of any civilians, including ballpark workers, as a precaution, before they were allowed to return shortly before 7 p.m.

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A search of the stadium determined the threat was unfounded.

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Officers investigate a bomb threat at Wrigley Field Sunday. (Chris Emma)

Officers investigate a bomb threat at Wrigley Field Sunday. (Chris Emma)

“Following our game this afternoon, we received a bomb threat and took swift action to clear the few remaining fans, players, staff and media from the ballpark. After a thorough search by law enforcement, no evidence was found to suggest this threat was credible,” the Cubs said in a statement Sunday evening. “We take safety at Wrigley Field seriously and are working with law enforcement authorities to pursue the person who initiated this threat.”

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The tens of thousands of fans who had been inside earlier were mostly gone at the time of the incident. The Cubs completed a four-game sweep of the San Francisco Giants.