The Independent Commission Against Corruption has raided the headquarters of the New South Wales Labor party.

Icac investigators arrived at the party’s Sussex Street base on Tuesday morning as part of an ongoing investigation.

A source said investigators accessed computers at the building during the raid.

Guardian Australia understands the raids relate to a Chinese Friends of Labor fundraising dinner held before the 2015 election.

In a statement issued on Tuesday afternoon, a party spokesman said the investigation related to “historic” donations.

“NSW Labor is aware of extensive media coverage today of an investigation into historic political donation matters,” he said.

“The donations in question were received in 2015 and have been fully investigated by the NSW Electoral Commission with the full cooperation of NSW Labor, including the provision of all relevant documents.”

A number of senior NSW Labor figures were taken by surprise after news of the raids broke. Many of the state’s Labor heavyweights are at the party’s national conference in Adelaide.

An Icac spokeswoman said the commission would not comment on operational matters.

Several figures from the NSW Labor Party have been linked to prominent Chinese political donors in recent years.

In 2017 former NSW general secretary and federal senator Sam Dastyari was forced to resign over his links to the Chinese billionaire Huang Xiangmo.

Dastyari helped elevate upper house MP Ernest Wong into the parliament. Wong is a former Burwood councillor known for his close ties to the Chinese developer community and ability to raise funds.

In June Fairfax Media reported that Australian security agencies believed Chinese government intelligence operatives had attempted to cultivate Wong.

Guardian Australia does not suggest either Wong or Dastyari are the target or subject of the Icac’s investigation.

Speaking to Sky News from the Adelaide conference, the federal Labor MP Matt Thistlewaite said he couldn’t comment on the “ongoing investigation” but he supported the work of Icac.

“It’s been a great body that’s uncovered corruption, investigated corruption and ultimately led to the prosecution of a number of individuals,” he said on Tuesday.

“They should be given all of the support to do the job that they’re established to do.”