MILL VALLEY (CBS SF) — A police search for a suspicious person near Tamalpais High School in Mill Valley that placed the school on lockdown Monday afternoon has ended, according to authorities.

Mill Valley police issued an alert about the police action and school lockdown at 2:33 p.m.

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A law enforcement source told KPIX that the Marin County Sheriff is involved and working a search in the area of the school on the 700 block of Miller Avenue in Mill Valley. So far, authorities have not located anything.

Authorities later said the search was for a suspicious person who had been seen in the area. Officers were dispatched to respond to a report of a subject was possibly carrying a rifle on Almonte Boulevard, to the rear of the school.

The person was described as wearing a black mask and black clothes and was possibly associated with with a white car, Mill Valley police said. Another witness reported spotting a similar suspect matching the description but did not see a weapon.

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An alert issued by Marin County Sheriff’s office stated that “All students are safe and the school is on lockdown.” The alert also cautioned residents “within 1/4 mile of Tam High” to shelter in place “with the doors locked.”

Video from Chopper 5 showed a number of police and sheriff’s units on the scene at the school.

The lockdown and shelter-in-place order were lifted at 4 p.m.

Police said Monday night that no criminal activity was verified and the suspicious subject has not been identified or located. Police received rumored reports of an associated armed bank robbery, but they were unfounded and unverified.

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“We appreciate the assistance of all the responding agencies that supported us today,” Mill Valley Police Chief Alan Piombo said. “We also appreciate the close coordination with School District officials, administration and teachers. We would also like to thank all parents and students for their patience and cooperation through this situation.”