Protesters have chained themselves to a gate and police have closed a road as demonstrations against the Roe 8 extension continue to disrupt work on the controversial project in Perth's south.

Two women chained themselves to the gate of the construction company contracted to undertake the clearing works at Beeliar Wetlands, stopping bulldozers from leaving the yard.

Tactical Response Group officers were called to remove them, and they were taken to Cockburn lockup.

Police said at least seven people were arrested on charges including trespassing, obstruction and refusing to give details to police.

Earlier officers were forced to close busy North Lake Road for about 90 minutes as up to 400 protesters demonstrated at the site.

Bulldozers resumed clearing trees around 10:30am.

Roe 8 forms the first stage of the Freight Link and is set to extend Roe Highway west of the Kwinana Freeway, with a proposed link towards Fremantle Port then set to follow.

The project has been controversial for economic and environmental reasons, with critics arguing it will cause irreversible damage to the andrewetlands and Labor calling for it to be halted ahead of the state election.

But earlier this month the Save Beeliar Wetlands group lost its last avenue of appeal against the highway extension, with the High Court refusing it special leave to appeal an earlier decision which revalidated environmental approvals for the project.