Bangkok: Australian filmmaker James Ricketson has been charged with gathering information that could jeopardise Cambodia's national security and could face up to 10 years in jail.

Authorities have held 68-year-old Mr Ricketson in custody for almost a week after a Cambodian media outlet published photographs of him flying a drone over a political rally in the capital Phnom Penh.

Court spokesman Ly Sophanna told the Phnom Penh Post that Mr Ricketson was charged on Friday with "receiving or collecting information, processes, objects, documents, computerised data or files with a view to supplying them to a foreign state or its agents, which are liable to prejudice the national defence".

The charge carries a prison sentence of between five and 10 years.

Confirmation of the charge came after days of conflicting reports about Mr Ricketson's fate, including that he would be only be charged staying in Cambodia illegally.

Cambodian authorities cracked down on country's media outlets and opposition parties ahead of local elections on June 4, including lodging court complaints against several journalists for seemingly routine reporting.

Non-government organisations were warned the government was closely watching them for any "bias" towards opposition parties.

Mr Ricketson, from Sydney, was flying the drone over a riverfront rally organised by the opposition Cambodia National Rescue Party.

For several years he has been working on a documentary about the party's former leader Sam Rainsy, who has been forced into exile to escape charges widely seen as politically motivated.

The Australian embassy in Phnom Penh said Mr Ricketson is receiving consular assistance but declined to comment further, citing privacy obligations.

Mr Ricketson studied at the Australian Film and Television School and has made several award-winning features and documentaries.

He has had a long-running dispute with Screen Australia.

Mr Ricketson is a frequent long-stay visitor to Cambodia, where he is known to donate food and provide other help to impoverished families, including rubbish dump scavengers.

He has campaigned for the release of children from orphanages and for the release of a British man convicted and jailed over child sex who he says is innocent.

In 2014 a Phnom Penh court gave Mr Ricketson a two-year suspended sentence for allegedly threatening to defame a refuge for girls run by an Australian charity.

He had been campaigning for the release of two girls from the centre whose mother said she wanted them to come home.

Mr Ricketson could not be reached for comment.