A search is under way for the boy, who followed his dog into floodwater at Cape Tribulation, in the Daintree, about 9.30am yesterday, police said. He was walking with his seven-year-old brother at the time.

"He disappeared in the water and his brother saw a large crocodile in the vicinity of his disappearance," police said in a statement.

Meanwhile, a search was continuing for two men who went missing on Saturday night at Silky Oak, south of Tully.

Police said a vehicle carrying seven people tried to drive through floodwater on the Bruce Highway at 9.30pm.

The car was washed away and five people were rescued, but two remain missing.

"We have SES from Atherton, Innisfail, Babinda and Gordonvale in flood boats conducting a search," said a spokeswoman for Emergency Management Queensland.

Monsoonal rain was moving south after causing flash floods in Cairns and Townsville and raising floodwater around isolated Ingham, where about 3000 homes were affected.

Northern Queensland has been declared a disaster zone as a result of cyclones Charlotte and Ellie, which dumped heavy rain on the region over the past few weeks. Forecasters warned that Mackay and Rockhampton could expect falls of up to 200 millimetres as the monsoonal trough headed their way.

"The whole system is moving further south, so Ingham is going into a period of lesser rainfall, a little bit of a reprieve," said a senior forecaster at the Bureau of Meteorology, Brian Rolstone. "[On Monday] the monsoon trough continues its movements south, and the bulk of rain will head down towards Rockhampton. We can expect local flooding to occur as that rain moves south."

But flood-affected residents in the north will have only a short reprieve. The bureau predicts a "vigorous" change will hit Fraser Island on Wednesday and merge with the monsoon trough at Mackay before making its way back up the coast.

"As time goes on, Thursday or Friday, Ingham will be back into it as [the trough] moves back over the top of them with major rain," Mr Rolstone said.

"The hopeful thing would be that it keeps on going and heading further north, but we're not too sure beyond Friday if it's actually going to do that."

The west of the state was also in for some heavy falls today, forecasters said.

In the 24 hours to 9am yesterday Ayr had 197 millimetres, Bowen 206, Ingham 83, Townsville 98, Cairns 123 and Cardwell 128.

The director of Queensland SES, Mark Dole, said authorities were keeping an eye on possible flooding in Rockhampton and Mackay and ensuring sufficient supplies in areas already affected by floodwater.

"Most areas that are in need have been catered for," Mr Dole said. "And there's also a lot of planning for areas that predict that they may, if they continue to be cut off, be in need of supplies in the next couple of weeks."

Yesterday the federal Treasurer, Wayne Swan, announced that cash payments were being made to North Queensland flood victims. Up to $1000 for adults and $400 for children in extreme distress was available immediately through Centrelink, he said.

Yesterday 50 homes in Ingham and two in Tully had been inundated.

Forty-one people were evacuated to Ingham High School while the town and its surrounds remained isolated as a result of the raised Herbert River.

The Bruce Highway was cut at several points yesterday, and there were flood warnings on the Burdekin, Diamantina, Don, Georgina, Nicholson, Flinders, Norman, Haughton, Herbert River, Tully and Murray rivers.