A new $86 million justice complex in Perth's southeast will provide three extra court rooms and a police station that can accommodate an additional 200 officers.
Premier Colin Barnett said there was a need for a new police station and court complex in Armadale because the existing facilities were 30 years old and too small to meet the needs of the area.
Construction would begin mid next year and the project had already been budgeted, which would be reflected in the mid-year review later this week, he said.
When it is complete in 2021, police numbers will be boosted from 80 to 315, and there will be five new court rooms.
Attorney-General Michael Mischin said the complex would ease pressure on the court system and enable the appointment of additional magistrates and court staff.
"By increasing the number of courtrooms and magistrates, we will be able to reduce the time between offenders being charged, convicted and potentially locked up," he said.
Opposition leader Mark McGowan said he supported the complex, adding the police station would operate 24/7 under his leadership, unlike the Liberal National government.
"It's an area with a lot of need, a lot of demand. We should have a police station that is open around the clock in Armadale," he said.
© AAP 2016