Police have arrested a 51-year-old man after packages containing suspicious white powder were delivered to Parliament House and the ACT Legislative Assembly.

The Belconnen man has been charged with five counts of using the postal service to menace and has been released on bail to face the ACT Magistrates Court on July 26.

Authorities investigating the suspicious white powder. Credit:Jay Cronan

Four of the charges relate to the powder scare that forced a three-hour lockdown of the Assembly building on Monday, an ACT Policing spokesman said, while the remaining count related to a similar incident at Parliament House.

Staff in ACT Opposition Leader Jeremy Hanson's first-floor office alerted authorities at about 11.10am after opening a package that contained white powder. More suspicious packages were discovered by staff in the second-floor offices of Chief Minister Katy Gallagher and Greens minister Shane Rattenbury.