Premier Annastacia Palaszczuk says life-threatening flash-flooding is under way and some rivers are still yet to peak, particularly in Logan and Gold Coast.
She said the Brisbane River is falling after peaking 3.85 metres on Monday morning, below the 2011 flood peak of 4.46m.
""It is still a significant event, and I think everyone would agree no one has seen this amount of rain in such a short period of time over our entire southeast catchment zone," Ms Palaszczuk told reporters.
"And I also want to extend my gratitude and thanks to the hundreds if not thousands of workers out there the SES crews, the police, our firies, our volunteers, all of the council workers."
Queensland Fire and Emergency services conducted more than 130 swiftwater rescues and responded to more than 2200 calls for help in the past 24 hours.
Seven people have already been killed and police are searching for three men missing in Brisbane, in Goodna, west of Brisbane, and in Esk, northwest of the city, on Monday.
Police Commissioner Katarina Carroll urged people across the southeast to stay in their homes.
"Please do not be complacent today. Be ... very careful if you have to move around. But if you don't, please stay at home," she told reporters.
"There is still a lot of water on the roads. There are so many roads cut off in Brisbane alone."
Ms Palaszczuk said more than 15,000 homes have been impacted in Greater Brisbane and 3600 in Gympie, north of the Sunshine Coast, and there were 1544 people in evacuation centres across the southeast.
The Mount Crosby Water Treatment Plant, which supplies drinking water to Greater Brisbane, was brought back online on Monday after flood debris clogged its filters on the weekend.
All trains in southeast Queensland, buses and ferries in Brisbane and trams on the Gold Coast have been suspended.
All schools in the southeast have been closed and people are urged to work from home.
Brisbane Lord Mayor Adrian Schrinner said the floods are "very different" to 2011 because the rain pummelled the region for five days.
"We've seen incredible amounts of rain," he told ABC Radio on Monday.
"With 2011 in some ways it was a dry flood. The rain had stopped well in advance and then we had several days notice that the flood was coming.
"It is very different this time. It came very quickly and the rain was so strong, so it is a different event."
Major flood alerts have also been issued for rivers in Gympie, Maryborough, Sunshine Coast, Noosa, Moreton Bay, Ipswich, the Lockyer Valley, Toowoomba, Darling Downs and the Gold Coast.
There are unconfirmed reports of looting in the Ipswich area with police investigating.
Prime Minister Scott Morrison was due to give a speech in Brisbane on Monday to the Queensland Media Club but the event has been postponed.
After smashing the southeast of the state, the severe weather is heading to the Gold Coast and NSW northern rivers district.
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