Geelong Grammar School will close four campuses on Wednesday as a precaution against the coronavirus pandemic.

In a letter to families and friends of the school, principal Rebecca Cody said the school council and executive and leadership teams had decided to bring term 1 to an early close as a pre-emptive measure.

"We deem this to be a timely judgment with a highly precautionary emphasis," she said in a written statement.

"Given our unique, predominantly residential context as Australia’s largest coeducational boarding school, with a student composition representing every state and territory, as well as 16 overseas countries, we are instigating an intentional and proactive staged unscheduled closure of our four campuses."