One detainee currently at the centre, Mohammad Anjum, is one of 39 men from Pakistan and Bangladesh who were found at Beagle Bay on the West Australian coast in February after arriving on a fishing boat from Indonesia.
"When we ask them how long we will stay here, how long we will go outside, what is our future — no one is saying this."
"If you attempt an illegal boat journey to Australia you will either be turned back or sent to Nauru," Ms O'Neil said.
Crossbench MPs including independent senator David Pocock, and North Sydney MP Kylea Tink are pushing the Albanese government to improve processing times, and prevent asylum seekers being left on Nauru for years.
Nauru detainee speaks out as new boat arrivals near 100. By Isabel Roe, ABC News