Western Australia's biggest high-speed interchange is now open, following the completion of works on NorthLink WA's most complex component - the intersection of Tonkin Highway and Reid Highway in Perth's north-east.

WA Premier Mark McGowan said the opening of Western Australia's biggest high-speed interchange is a real game-changer for our growing city.

"NorthLink WA is creating thousands of jobs for Western Australians and they should all be commended for their outstanding work on what is a very large and complex project," Mr McGowan said.

"My Government has a comprehensive plan to deal with congestion on Perth roads. Our METRONET plans are taking shape, and they are being complemented by important upgrades to our road network."

The opening of all remaining ramps on the interchange means motorists can now enjoy a free-flowing journey in all directions, saving time and improving safety.

Minister for Cities, Urban Infrastructure and Population Alan Tudge said NorthLink WA is a vital, state-of-the-art transport link between Morley and Muchea diverting 80 per cent of heavy vehicles away from local roads and improving amenity in the Swan Valley for residents and the 600,000 tourists visiting the area each year.

"Road users travelling from Kewdale to Muchea can potentially avoid up to 16 sets of traffic lights, two railway crossings and 21 speed limit changes," Mr Tudge said.

A new flyover will also replace the temporary roundabout that has been in place at Beechboro Road North, enabling traffic to go over Reid Highway.

WA Transport and Planning Minister Rita Saffioti said this is yet another boost for north-eastern suburban residents, who have been crying out for better transport links.

"We now have several transport projects nearing completion, underway or being planned," Ms Saffioti said.

"Once complete, NorthLink WA will provide much needed extra road capacity to Perth's north-east, which is a priority for the growing community of Ellenbrook."

Motorists travelling north on Tonkin Highway will now be able to travel on the new section of road as far as the Gnangara Road T-junction, about 7.5km north of the Reid-Tonkin interchange.

Member for Pearce Christian Porter said, once the Gnangara Road intersection is completed in coming weeks, the journey along the new alignment will be able to continue onto Gnangara Road without the interruption of the signalised T-junction.

"This means commuters around Ellenbrook will have drastically improved journey times," Mr Porter said.

Driving conditions are constantly changing and finishing works are still being completed so please pay careful attention to the new configuration and obey the signs.

Until the highway is open to Gnangara Road interchange, heavy vehicles will use Reid Highway and Great Northern Highway.

An animated video with the additional movements has been created to help motorists navigate the changes.