Senator McKim said his passport was confiscated after he tried to enter the East Lorengau facility on Thursday morning.

"I now have my passport back, but police and immigration then stopped me on the street and I've been informed that a deportation notice will be issued to me later today," he tweeted.

"I was granted a 12 month multiple entry visa by the PNG government and am here legally.

"Every kina spent here on refugees has been authorised by the Australian parliament, and there should be accountability on how it is spent. That accountability and truth telling is my job."

Senator McKim is visiting Manus Island to mark six years since the Rudd government reintroduced offshore detention for asylum seekers who arrived by boat.

"I have always treated police, immigration and all PNG people with respect, and obeyed their laws," he said.

"Offshore detention is not of their making, and has been very difficult for many of them."

Around 450 asylum seekers remain in PNG and another 350 are being held on Nauru.

"For six years the Australian government has played politics with the lives of innocent people in our care on Nauru and Manus," Human Rights Law Centre executive director Hugh de Krester said.

"After so much suffering, the Morrison government must act now to allow these people to rebuild their lives in safety and close the camps permanently."

Australian Associated Press