A Nepali tour operator says he fears that 15 Australians trekking with his company in a valley ravaged by flash flooding have died.

Sagar Pandey, the founder and chief executive of Himalayan Glacier Trekking, said he had lost all contact with his tour group of 47 people, which included 15 Australians.

The missing Australians ranged in age from 11 to 64 and the group was believed to include two families of four from New South Wales.

At least 165 people have died and hundreds more are missing after the devastating floodwaters surged through the valley on both sides of the border with Tibet.

Pandey said he had since flown by helicopter over the Rasuwa area, where the tour was staying, and said he had little hope they survived.

“To be honest … you would think there was no human civilisation there at all.

“The flash flood swept away everything, everything, you couldn’t see any human creations.

“Still, I have a hope, but like 1%; the rest I don’t have a hope, they are missing and missing and missing.”

Pandey, who is also the president of the Trekking Agencies’ Association of Nepal, said he had been coordinating with other local tour groups, which had also lost contact with their guides in the area.

Among those groups were operators who had arranged tours for Australians, he said.

Pandey said his missing group included tourists from the UK, US, Canada and Singapore and his guides.

They had made their way to the valley after a drive of about seven hours from Kathmandu, and had been expected to head towards the border with China at about 8.30am on the day the flood struck.

Pandey said that on his helicopter flight he noticed about 100 people on higher ground, who he believed were local people who narrowly escaped the carnage.

Guardian Australia has confirmed the missing Australians include people from Sydney’s north-western suburbs, including separate families who were travelling together.

The number of missing Australians is based on those reported by tour groups in the area, foreign minister Penny Wong confirmed.

Kathmandu Holiday Tours and Travels is reporting one missing Australian, and was contacted for comment.

The Trekkers’ Society, which posted a statement confirming 92 travellers including 77 foreign nationals had gone missing, was also contacted for comment. They did not specify in the statement if any Australians were among those missing.

“I can only outline the numbers that we are aware of to date … but I would say the number is at least 34,” Wong said.

“Those numbers are being provided … through tour operators.

“We will continue to try and ascertain if there are any other Australians who are not accounted for and over and above the 34.”