Floodwaters in Townsville on Friday.

Queensland's north continues to be swamped by exceptional rainfall.

Water from Townsville's bulging dam could flood up to 100 homes under a risky plan to save the city from widespread flooding.

Major releases are underway from the Ross River Dam but Townsville mayor Jenny Hill says there are no guarantees the plan will work.

Between 90 and 100 homes downstream from the dam are being evacuated, as the city deals with a one-in-100 year event.

Water releases will exceed what's usually allowed under Townsville's emergency action plan but Ms Hill said authorities had no choice with more days of torrential rain ahead.

"What we're trying to do is to get ahead of the system, so we reduce the risk of any further flooding in the city - but that's not guaranteed," she told reporters on Friday.

The dam is currently at 180 per cent of capacity - its highest level since it was built 48 years ago.

All three dam gates are open and spilling and the Ross River is dumping a record amount of water into the sea.

"We haven't taken this decision lightly," the mayor said.

Soldiers have been mobilised to help sand-bag vulnerable properties.

Authorities have gone door to door telling people they should leave at-risk homes in Cluden, Rosslea, Hermit Park, Oonoonba, Idalia and Railway Estate.

Fifty houses have already sustained flood damage, and that's expected to rise, and 28 rescues have been carried out so far.

Elly Carpentier lives at hard-hit Bluewater, north of Townsville, and says her home flooded in the time it took her to take her kids to school and return home.

"It came up three metres in 30 minutes. My house was submerged under water, that's how quick it was," she told AAP, saying she got caught out while taking her kids to school.

"My husband and four-year-old were trapped inside and had to be rescued by swift water crews."

Huge downpours cause major flooding and evacuations near Townsville

About 100 families have so far sought help and support at Bluewater Community Centre.

"We've had few families through that have lost pretty much everything," centre worker Darla Astill told AAP.

"People have had to just sit and watch cars, tractors, containers, ride-ons and all sorts of stuff just floating in the creek."

Dr Richard Wardle from the Bureau of Meteorology said the Townsville area had been swamped with more than a year's worth of rain.

"The annual rainfall for Townsville is 1.1 metres. We're seeing more than that at the moment. We're going to see places get two or three times their summer average rainfall amounts."

Some areas could get up to 400mm a day, for the next few days, due to a very active and slow moving monsoon trough.

Source AAP - SBS