Lives are under threat as flash flood water coursing down streets in the Queensland city of Toowoomba, west of Brisbane, has turned the street into rivers, the Australian Associated Press (AAP) reported on Monday.

Video footage shows vehicles, some with drivers still trapped inside, being swept away and thrown into the sides of other cars and caught up in trees.

One pedestrian could be seen trying to dodge cars charging along what was once a street.

Deputy Police Commissioner Ian Stewart said lives were under threat.

Witnesses have told police up to two meters of water swept through parts of the city after about three hours of extreme rainfall from about midday.

Queensland Premier Anna Bligh said a "massive deluge" had hit the city.