The department of foreign affairs and trade has been in contact with more than 200 of the 549 registered Australians as travelling in Nepal, but "challenging conditions" have made it difficult to contact others, the Canberra Times reported.
Among the missing is 26-year-old volunteer James Brinson, from Sydney, who worked with World Vision in Dhaka to provide water and sanitation.
The Red Cross Family Links web site said the last time he was heard was on April 20 in the Indian state of Sikkim, which experienced landslides after the quake.
Among others unaccounted for were 20-year-old Zachary Sheridan from Adelaide, who last contacted his family on April 11 from near Mount Everest, and Chatswood woman Isabel Baudish, 25, who was trekking the Annapurna Circuit with a friend after doing some volunteer work in India.
Australian Foreign Minister Julie Bishop on Monday said the government had pledged $3-million assistance package to Nepal and also assured to find the missing Australians.