Australian Prime Minister Kevin Rudd has condemned the latest developments in Fiji, saying they turn the Pacific country into a military dictatorship.

Fiji's President Ratu Josefa Iloilo on Saturday swore in armed forces chief Commodore Frank Bainimarama as the troubled country's Prime Minister, a day after the President suspended the constitution and fired judges who declared the military leader's earlier government illegal.

President Iloilo also declared a 30-day state of emergency, limiting freedom of speech, expanding police powers and curbing media reporting.

Police have been given powers "to control the movement of people" and Mr Iloilo's decree means the state can stop any broadcast or publication it deemed "could cause disorder ... promote disaffection or public alarm or undermine the government or state of Fiji".

The radical moves ensure Commodore Bainimarama retains control over the South Pacific nation despite a Court of Appeal ruling on Thursday that the 2006 coup in which he seized power was unlawful, and so was his government.

The turmoil marks the latest chapter in a long-running political crisis in the country of 800,000 people that has become increasingly unstable and poor after four coups in the past 20 years.

The changes have drawn international condemnation, with Australia, New Zealand, the United States, the United Nations and the Commonwealth calling for a return to democracy.

Mr Rudd deplored the latest developments in Fiji as he returned home from the cancelled Asean summit in Thailand.

"Australia condemns unequivocally this action by the military ruler of Fiji to turn this great country, Fiji, into virtually a military dictatorship, with the suspension of freedom of the press and actions which undermine prosperity for the ordinary people of Fiji," he said.

- AAP