Flood waters in the city of Rockhampton in Queensland are hitting what is expected to be their peak level.

More than a week of pounding rain has left much of northeastern Australia under a sea of muddy water that is making its way through river systems towards the ocean.

The swollen Fitzroy River is expected to reach the second-highest level on record on Wednesday in the largest affected community of Rockhampton before finally beginning to subside.

Some 400 homes may be inundated, and the river could remain above flood levels for at least a week. Up to 500 people who live along the River Fitzroy have evacuated their homes.

Police in the flood-affected areas of Rockhampton have been patrolling in boats around the clock to make sure looters stay away from abandoned homes.

Air and rail links to the city of 75,000 people have been cut and only one main road remains open.

The flooding is already having an impact on Queensland's economy, ruining crops and closing most mines.

Worse could be to come. Around 350 miles away from Rockhampton, the town of St George is preparing itself for flood levels reaching up to 14 metres.