Concerns have been raised about the 25-year-old, who was working as an English teacher in Sendai, ravaged by a 10-metre tsunami on Friday.

His mother, Mary, from Point Cook on Melbourne's southwestern outskirts, said she last heard from her son at 4.45pm (AEDT) on Friday, just hours before the tsunami hit, following an 9.0-magnitude earthquake.

She said someone had since reported on a Facebook page that they had seen her son, but she was concerned that he had not yet made contact.

Mr Rudd said today that while there was no further information on the case, the Department of Foreign Affairs and Trade (DFAT) was working with Japanese authorities to find Mr Briffa.

"We will not spare any effort in tracking down the whereabouts of each and every Australian that we haven't been able to identify so far," Mr Rudd told Channel 9.

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As of 5.30am (AEDT) today the Consular Crisis Centre in Canberra had taken nearly 7000 calls from the Australian public and 2000 of those had been confirmed as safe, he said.

"People should not be concerned by the gap, it takes time to work these things through," he said.

Mr Rudd said people concerned about family and friends should first try to contact them on mobile phones, followed by landlines and if they still fail to make contact, should provide all details to the DFAT Crisis Centre.

Mr Rudd said Australia's 72-strong search and rescue team as well as translators from the Australian embassy were in Japan and would be on the ground and ready to assist in a town south of Sendai later today. 

Australia's ambassador to Japan Murray McLean says it's difficult to know exactly how many Australians have been affected by the earthquake.

"We really, honestly, do not know how many Australian's were in Japan on the day of the big earthquake," he told ABC Television.

"The numbers are fluctuating."

Attorney-General Robert McClelland says 102 of the 234 Australians registered as being in the quake-affected areas have been found safe.

Advertisements are running on radio and television to determine the whereabouts of those who have not been located.

Of the 11,000 Australians believed to be in Japan, 1964 have been confirmed as safe.

Search-and-rescue teams

An Australian team of 78 search-and-rescue personnel arrived in Japan this morning. The team included paramedics, interpreters and rescue dogs.

Mr McClelland said the team are heading to an area about 200km north-east of Tokyo.

Australian liaison officers would be talking to Japanese authorities about the need for additional services such as medical assistance, sanitation and desalination.

"We're basically indicating wherever we can constructively assist that we will," Mr McClelland told ABC Radio, adding it was likely help would be needed with victim identification.

Mr McClelland said the teams would be based in Miyagi Province, 135km north-east of the Fukushima nuclear plant.

"As precautions ... they've been given some special equipment including (radiation) detection equipment."

Australians planning to travel to Japan have been told to reconsider.

Mr McClelland said Australians working in Tokyo and other major cities away from the damaged area would continue to work as normal.

"But certainly we think instinctively those in the damaged area will want to get out."

Mr McClelland said every assistance was been given to Australians who want to leave.

Offices of the Department of Foreign Affairs and Trade have been set up at major airports in Japan.

People requiring assistance can ring 1300 555 135.