The Bureau said there had been "extremely heavy falls" since 9am yesterday, with 506mm recorded at Ingham Pump Station, 415mm at Halifax, 309mm at Cardwell Gap and 271mm at South Mission Beach.
Townsville has received more than a metre (3.3ft) of rain in the past week - more than 20 times the average for the time of year.
Opening the spillway would release up to 2000 cubic metres of water per second from the Ross River Dam, over nine and a half hours overnight.
Officials earlier warned that up to 20,000 homes could be flooded.
Premier Annastacia Palaszczuk said the severe weather would move south, putting Mackay in the warning area.
One of the city's five evacuation centres is now full and unable to accept any more evacuees, and crocodiles have been spotted outside suburban homes.
Dozens of other locals have posted via social media they're perched on kitchen benches and their rooftops awaiting rescues.
Police officers wade through flood waters in Townsville.
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 vehicle.
"In Queensland, of course, we're used to seeing natural disasters, but Townsville has never seen the likes of this".More news: Manchester United ready for 'tough' and 'enjoyable' top-four fight, says Solskjær
"A lot of young families, they've worked so hard to get themselves into these homes and to see them just damaged so badly, it must just be heartbreaking", he said.
The bodies were discovered by police in a storm water drain at Aitkenvale as the floodwaters started to clear across the city on Tuesday morning.
"Residents still in their homes in these suburbs should move to the highest ground in their dwelling".
Australian man Andrew Roberts is more anxious about being eaten by a crocodile in his Townsville home than chest-high water surging through the ground floor.
Townsville mayor Jenny Hill praised the work of emergency services but said "last night was rough".
About 10,000 people have already lost power since Friday - and more power outages due to public safety concerns are likely.
A record 1.16 meters (3.8 ft) of rain has fallen across the Townsville area over the past seven days, with another 100 millimeters expected to be dumped over the area on Monday, the Bureau of Meteorology said.
Sasha Ngamoki posted photos on social media to pass on her gratitude to Chris from Armesto's Transport and BM Webb who pulled her family out of a risky situation.
Ignazia Graziella Grace, nee Grace Grace, Minister for Education and Minister for Industrial Relations, has said state schools in Townsville and surrounding areas will remain closed on February 5.