They climbed on to the vehicle's roof about 2am (CST), but were swept off into the swollen river, clinging onto a tree branch about 50 metres downstream before being rescued.
Two families northwest of Katherine were forced to scramble onto the roofs of their properties after more than 30cm of rain fell on parts of the Northern Territory on Tuesday morning.
And there were other close shaves.
NT Police Commander David Proctor said a couple escaped from their car after it was washed from a bridge over the Cullen River, south of Pine Creek.
"Several other motorists are stranded between Katherine and Pine Creek with the Stuart Highway cut by rising flood waters at Edith Falls River and the Cullen River," he added.
Crocodiles were also a concern.
"It's the wet season and this is the Northern Territory, so I wouldn't want to go swimming in any of it (the flood water)," a Northern Territory emergency services spokesman said.
Cyclone Grant was downgraded to a tropical storm on Monday.
Torrential rain is predicted to continue falling across eastern parts of the Top End and emergency services are expecting to remain on high alert for at least the next 24 hours.
The Bureau of Meteorology said the storm centre was about 250km southeast of Darwin on Tuesday and moving southeast.
It was expected to turn east on Wednesday and move toward the Gulf of Carpentaria.
The bureau said Grant could make a comeback as a tropical cyclone as it passed over the gulf on Thursday.
- AAP
