Police have carried out raids at several properties across Sydney to disrupt plans for terrorist attacks in Australia, Prime Minister Malcolm Turnbull says.

Four homes across Sydney were raided by heavily armed police on Saturday evening as part of a terrorism investigation.

Australian Federal Police (AFP), ASIO and New South Wales Police conducted operations in the inner-city suburb of Surry Hills, and the south-west suburbs of Lakemba, Wiley Park and Punchbowl.

The AFP said four men had been taken into custody.

A source has told the ABC the plot was believed to relate to an attack on an aeroplane but it was understood police are trying to work out whether the threat was credible.

A Surry Hills resident left her home saying her husband and son were taken into custody in raids. ( ABC News Jake Sturmer )

A woman who told the ABC her son and husband were arrested after her Surry Hills house was raided denied they had any links to terrorism.

"I love Australia," she said as she was accompanied to a waiting car by police.

The Prime Minister's Office released a statement saying the operations were "designed to disrupt and prevent plans to undertake terrorist attacks in Australia".

"I have been kept closely briefed on the progress of the operations by the heads of our relevant security agencies," Mr Turnbull said.

"However, as the operations are ongoing, it is inappropriate to provide further detail at this stage."