The search for a German couple missing in the outback near Alice Springs has been suspended until first light on Monday
A ground and air search was launched on Sunday after a ranger found a car thought to belong to the man and woman, aged in their 70s, at Trephina Gorge, Northern Territory police say.
A police spokesman said the couple had not been found by about 7pm on Sunday and the search would be suspended until first light on Monday.
The ranger who found the car said it had been in the car park for two days, Territory Duty Superintendent Rob Burgoyne told AAP.
"He followed some tracks to a fence line which had recently been washed away and he believed that there were two persons who had walked from the vehicle," Supt Burgoyne said.
The couple arrived in Australia at the start of the month and hired a car from the Alice Springs airport on February 9.
Sometime in the next day, they drove more than 70km east to Trephina Gorge.
"We have grave concerns for their safety because it's been 40 degree heat down in that area and because these people are of advanced age," Supt Burgoyne said.
Authorities are contacting the German consulate to try and find out more about the couple, including any possible medical conditions and to contact their family.
A helicopter was sent to scour the area on Sunday while police, SES personnel and a park ranger searched on foot.
"There should be some water lying around so even if they didn't take a lot with them, if they've got enough bush sense they should be right," Supt Burgoyne said.
"But these temperatures are very high and I certainly wouldn't want to be walking any length of time in those conditions."