"International troops have secured the airport in Tonga after days of rioting, and commercial flights are to begin evacuating foreign nationals from the island on Sunday," he said.
Downer played down the suggestion that foreign nationals on the island were in a panic to get out.
"Leaving the island is up to them. Some of them feel a bit nervous depending on who they work for ... and others feel perfectly safe."
Police and soldiers from Australia and New Zealand arrived on the impoverished Pacific island on Saturday following street violence that started on Thursday, which killed at least eight people and destroyed most of the capital's business district.
Downer told the Australian Broadcasting Corp television late on Saturday: "The situation in Tonga is quiet at the moment, fortunately, and has been since the riots took place the other night. Hopefully, there won't be any more problems and we'll be able to withdraw fairly soon."
Sixty soldiers and 10 police officers from New Zealand and 85 Australian soldiers and police, including forensic experts to identify bodies charred in the riots, arrived in the kingdom's capital, Nuku'alofa, on Saturday.
The troops will secure infrastructure, including the airport, power stations, broadcasting systems and government buildings. Downer said any of the 300 Australians in Tonga could be evacuated if they wished.
The violence was triggered by anger that parliament might finish this year's session without settling plans to introduce reforms that would give democratically elected politicians a parliamentary majority over royally appointed legislators.