Opposition immigration spokesman Scott Morrison has demanded an explanation of why news of the arrival on Tuesday night was only made public on Wednesday.
Morrison claims the news was buried for at least 24 hours, while the PM was in Darwin to spruik her new border protection policy.
Authorities have intercepted a boat carrying 43 asylum seekers and three crew in waters off Australia's northwest coast.
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The boat was intercepted west of the Ashmore Islands late on Tuesday, just hours after the PM announced changes to Labor's border protection policy.
Those on board were taken to Christmas Island to undergo security, identity and health checks and their reasons for travel will be established.
Gillard has announced a shift in the federal government's asylum seeker policy, including pushing for a regional refugee processing centre to be established in East Timor.
She also announced a freeze on the processing of asylum seekers from Sri Lanka, introduced in April, would be immediately lifted.
