NT Police will launch a flood boat in the Hugh River to search for the car.
The tourist was thought to be from Asia but the nationality has not yet been confirmed.
Meanwhile, the number of people lost in a remote area of the outback for almost two days now has doubled, police have confirmed, with a child among the group.
Initially, it was thought three adults had gone missing while in a car between Kiwirrkurra and Kintore, remote settlements on either side of the Western Australian/Northern Territory border.
However, it is now thought two cars were on the road with the second containing two adults and a child, the age of whom is unknown.
"We're seriously concerned for their welfare," Mr Muldoon said.
Fears were raised when the group, which set off from Kiwirrkurra, a community in Western Australia's Gibson Desert, on Christmas Day failed to reach Kintore.
The six people were divided between a Ford Falcon and a Nissan Navara.
The journey usually takes eight hours, however the party has not been seen for almost 48 hours.
There are concerns the car was caught in the ferocious weather conditions that have enveloped the centre of Australia. More than 230mm of rain fell in the area around Kintore in a 24-hour period over the Christmas weekend, causing flash floods across the desert.
The deluge broke all records, with the previous highest daily rain total, a significantly lower 127mm, recorded in March 2006.
Eighty-five people spent Christmas night at Kintore school after they were evacuated from their homes following flash flooding on Christmas Day, the NT News reported.
It is estimated 40 per cent of all homes in the town of about 500 people were damaged by the flood in some way.
NT Police said a search was planned for the group but the atrocious weather was hampering efforts with roads between Kintore and Kiwirrkurra cut off by flood waters.
"Because of the roads, we have to use air support but low cloud clover is making it difficult to get safely into the air," an NT Police spokesman told news.com.au.
With conditions improving, the Police air wing has now been sent to the area to search for the six.
Muldoon said the remoteness of the area meant there was no phone coverage to check on the group's welfare. They were not thought to be carrying a satellite phone or an EPIRB beacon.
A deep low-pressure system has delivered so much rain to the area, normally dry Uluru was cascading with waterfalls.
The floodwaters are now receding from Kintore, but concerns remain for the three missing people with a severe weather warning still in place for the south of the Territory.
The Bureau of Meteorology has warned that fresh heavy rain could lead to further flooding over the Lasseter and Simpson districts with damaging gusts of up to 90km/h.