SAN FRANCISCO (CBS SF) — Fire fighters responded to reports of smoke in the Muni tunnel near the Civic Center station Monday morning.

Crews determined the smoke was due to debris in a fan room and the problem was quickly resolved.

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Fire officials were warning riders to avoid the area and use shuttles for alternate transportation.

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A Muni spokesperson said service was halted around 9:35 a.m., and resumed by 9:45 a.m.