A radical proposal allowing police to hold terrorism suspects without charge for up to 14 days has received the backing of Victorian Premier Daniel Andrews.

He said civil liberties were a "luxury" in the face of the "very real terror threat" Australia is facing.

"We are going to have to curtail the rights and freedoms of a small number of people in order to keep the vast majority of Australians safe," he said.

"That is challenging. But it is necessary."