Emergency crews have been stretched to the limit in flood-hit Townsville, with hundreds of people still waiting for help and evacuation centres filling up fast.

Unprecedented water releases from the city’s swollen dam have sent torrents of water down the Ross River and into the city, swamping roads, yards and homes.

Crocodiles have been spotted in suburban streets, and the water is teeming with snakes.

It’s unclear how many more homes may have been inundated. On Sunday the figure was between 400 and 500.

But that was before dam releases were doubled in anticipation of more rain, sending almost 2000 cubic metres of water per second charging out of the Ross River Dam.

Authorities have warned between 10,000 and 20,000 homes could be at risk.

With days of more rain ahead, the crisis is far from over and the premier says forecasters are closely watching the monsoon trough amid fears it could form into a cyclone if it moves off the coast.

“This system, if it moves out to the sea, it could develop into a cyclone,” she told the Seven network on Monday.

“These are early days and we won’t know for certain until the next few days.”

The Bureau of Meteorology has also warned that tornadoes could form, with gale- force winds seen in Townsville overnight.

The premier said emergency crews responded to more than 200 calls for help overnight, with about the same number still waiting for help on Monday morning.

The weather was atrocious overnight, with two police engaged in evacuation work rescued themselves after fast rising flood waters trapped them and washed away their patrol car.

They were rescued after spending half an hour clinging to trees.

“It was just bucketing down last night ... and the wind gusts were huge. It was a tough night,” the premier said.

Camera Icon A resident walks through floodwaters with a bicycle in Hermit Park, Townsville Credit: AAPIMAGE

Water releases from the dam sparked emergency flood alerts late on Sunday, with residents in 21 Townsville suburbs told to move to safety.

The premier said the dam had been been managed well, and the council did what it had to do.

“That water needs to go somewhere. From what I can tell, they’ve done everything from the book,” she said, saying the peak was yet to come in the next day or two.

“Townsville has never seen the likes of this.”

About 1000 people were now in evacuation centres, with one of five centres now full. The council will decided of other centres need to open on Monday.

Schools in Townsville remain closed and a decision will be made early on Monday about whether to reopen the city’s airport after all flights were cancelled late on Sunday.

The monsoon trough that’s been dumping flooding rain on north Queensland’s east coast, and drought-hit parts of western Queensland, will drive the state’s emergency for days to come.

Intense rain with significant flash flooding is expected between Ingham and Bowen, and possibly as far south as Mackay, extending inland to Mt Isa near the Northern Territory border.