Suspicious envelope at NSW govt offices

A suspicious envelope containing white powder has been found at the building housing the NSW premier's office in Sydney's CBD.

Police on Tuesday morning responded to reports of a suspicious package at the state government ministerial offices on Martin Place.

AAP understands an envelope was opened in the mailroom and found to contain white powder stuck to sticky tape.

Fire and Rescue NSW sent seven crews to the scene to deal with the suspicious "substance" including two hazmat crews wearing protective suits.

Their job was to test the toxicity of the substance and make it safe before handing it to police.

NSW Police are now forensically examining the powder.

Officers blocked off the main entrance to 52 Martin Place and were stationed inside the foyer.

Government staff could still access their offices, however, via an alternative entrance.

Attorney-General Mark Speakman told reporters outside the building he was unaware whether the item was addressed to the premier's office as was initially reported.

"If that's the case, it's concerning," he told reporters.

"But I don't know. I'm not privy to the details."

Emergency services declared the area safe shortly after midday on Tuesday.

Premier Gladys Berejiklian later told reporters: "I always feel safe with the police in control and in charge. That's all I'll say on that."