Police have charged a NSW Treasury staff member with stealing sensitive documents following an investigation into an alleged data breach at the department.

NSW Police Force’s cybercrime squad launched the probe after the state government reported the matter on April 19.

“Police received a report that more than 5600 sensitive government documents had been allegedly accessed and downloaded by a staff member,” the force said.

“Following inquiries, about 1.30pm [on April 20] strike force detectives arrested a 45-year-old man in Sydney’s CBD ... The 45-year-old man was charged with access/modify restricted data held in computer.”

The suspect was granted conditional bail to face Downing Centre Local Court on June 3.

Electronic devices including a hard drive were seized when detectives searched a home in Homebush West, according to the police statement.

“Police believe all the alleged stolen data has been located and secured and there was no external compromise to the agency’s system,” the force said.

The NSW government declared the alleged breach a “significant” cyber incident on April 20, a statement from Treasurer Daniel Mookhey said.

“Internal security monitoring detected a suspected transfer to an external server of a substantial cache of documents containing confidential commercial and financial information,” he said.

“The files cover multiple NSW government departments and projects.”