Thousands of Marin County students learned Thursday night that their campuses would be closed for at least two weeks as a precaution against coronavirus transmission.

Tamalpais Union High School District announced its five campuses will close starting Friday. The decision affects more than 5,000 students at Redwood, San Andreas, Sir Francis Drake, Tamalpais and Tamiscal high schools.

Classes are scheduled to resume March 30, a Monday. Staffers will be on the campuses between 8 a.m. and 3 p.m. Friday so students can pick up instructional materials.

“We did not take this decision lightly,” the district said in its announcement. “There are no known cases of diagnosed coronavirus (COVID-19) among TUHSD staff or students at this time. However, as the coronavirus (COVID-19) situation has unfolded and we gathered more information at the state and local level, it has become clear that the most responsible action, at this moment, is for us to take a proactive versus reactive approach to social distancing and other containment measures.”

Also Thursday night, the Ross School District announced the elementary school would be closed starting Friday. Classes are set to resume March 30.

Michael McDowell, superintendent of the Ross School District, said in a note to parents that “our decision to return will be based on a variety of factors.”

“We will continue to communicate with families on the status of the situation, the school, and our next steps in opening our doors as soon as possible,” he said.

The private Branson School in Ross announced the cancellation of on-campus activities and off-campus events for two weeks beginning Friday. The school planned to transition to online studies beginning Wednesday.

“We hope to be able to return to school on March 30, so that we can have a week of classes before we go on break on April 3, but at this time we do not know if that will be possible,” headmaster Chris Mazzola wrote.

San Domenico School, a private K-12 campus in San Anselmo, will conduct distance learning following Friday’s school holiday. Administrators did not immediately set a return date.

The closure announcements came two days after a similar decision for seven Catholic schools in Marin County in a regional school shutdown by the Archdiocese of San Francisco.

All the Marin schools planned to switch to online study arrangements.

The Marin school closure announcements followed a wave of others in the Bay Area on Thursday, including the massive San Francisco Unified School District and the West Contra Costa Unified School District.

As of Thursday, three confirmed coronavirus cases have been reported in Marin County, according to the public health department. No deaths have been reported in Marin.

Statewide, nearly 200 people have tested positive, with half of those cases in the Bay Area. The respiratory disease has sickened more than 125,000 and killed more than 4,600 worldwide.

Bay Area News Group contributed to this report.