Armed with rainbow-coloured chalk and umbrellas, hundreds of people rallied behind the Safe Schools Coalition in Melbourne's CBD on Thursday evening.

The crowd gathered at the State Library despite the drizzly weather in a show of support for the program, which aims to promote acceptance of gay, lesbian, bisexual and transgender students.

In recent weeks, the program has been criticised by conservative politicians and the Australian Christian Lobby, who have argued the Safe Schools teaching manual contains inappropriate material. Prime Minister Malcolm Turnbull subsequently ordered an independent review of the program last month.