Residents in low-lying parts of Rockhampton have been warned to prepare for what could be the biggest flood to hit the central Queensland city in almost a century.

Police Commissioner Ian Stewart has warned the Fitzroy River could reach 9.5 metres at Rockhampton on Friday, which would be the biggest flood to hit the city since 1918.

Mr Stewart warned those in low-lying areas to start moving their property to higher ground on Saturday.

"I'd encourage people to move now. Don't wait until Monday or Tuesday," he said on Saturday.