With up to 500 homes already under water in Townsville and surrounds at the weekend, another heavy deluge of rain pushed Ross River Dam levels to almost 250 per cent capacity, forcing authorities to open the floodgates.

In the 24 hours to 5am on Monday, the State Emergency Service received 850 calls for help, most from Townsville residents asking for sandbags and supplies.

Police officers had rescued one group of people on Sunday night and were going back for another, on Charters Towers Road in the Townsville suburb of Hermit Park, when the conditions changed and they needed to be rescued themselves.

An hour after police called for help, rescue crews got them to higher ground on the other side of the road. Both officers were injured.

Meanwhile, Townsville resident Erin Hahn posted a photograph of a crocodile outside her father's house in Mundingburra, and urged people to "stay out of the water".

In a separate incident, two more people were plucked from the raging floods by rescue crews in Townsville overnight.

The pair were stranded on the roof of their car as the water rose around them at the intersection of Bayswater Road and Sussex Street in Hyde Park.

A rescue boat reached them about 8.50pm and they were heading to dry ground 10 minutes later.

Close to 2000 cubic metres of water was surging out of the Ross River Dam every second after 9pm on Sunday, prompting warnings from the Bureau of Meteorology to residents in low lying areas.

The dam level had dropped to 238 per cent by 6am on Monday but there were fears that between 10,000 and 20,000 properties could be at risk of inundation.

Power was cut to thousands of homes in the north Queensland city, and hundreds of people who have been forced from their homes by waist- and chest-deep water were taking refuge at evacuation centres or with family and friends on higher ground.

Premier Annastacia Palaszczuk said the flood disaster was far from over, and weather forecasters said between half a metre and a metre of extra rain could fall on the east coast in the coming days.

The Ross River at Aplin Weir was at 3.11 metres and rising late on Sunday night, with authorities expecting it to reach four metres.

The extra water could flood more homes along the river, with people in several suburbs including Rosslea, Hermit Park and Townsville City told to move to higher ground immediately.

Townsville Airport announced it had cancelled all flights in and out just after 6pm due to safety concerns and it remained closed on Monday morning.

The monsoon trough that had been dumping vast amounts of rain on the state's north for a week has rewritten Townsville's record books.

In seven days, the city copped a staggering 1012 millimetres, eclipsing the previous record of 886 millimetres set in 1998, when vast swathes of the city went under.

Authorities have pleaded with Townsville residents still in their homes to get ready to move.

- with AAP