An over-the-top police presence led to tensions escalating at a protest at the site of the proposed Roe Highway extension, according to the WA Greens.

In Parliament, Greens MP Lynn MacLaren stepped up her criticism of the police presence at Tuesday's protests at Bibra Lake, which the Government said about 37 officers attended.

About 60 people confronted workers at the site at the Beeliar Wetlands, with some blocking the path of drilling and support workers from Main Roads.

There were also verbal confrontations between protesters and workers, who the Government said were doing monitoring ahead of the proposed extension of Roe Highway from the Kwinana Freeway to Stock Road.

The so-called eighth stage of Roe Highway has proved highly controversial, with criticism over the cost and benefit as well as environmental concerns.

The protest was the latest in a long string of demonstrations staged since the project was first announced, but Ms MacLaren said this one was sparked by the heavy presence of officers.

"The Police Minister implied that 37 police responded to an event, when the truth of the matter is an event occurred because there was 37 police down there," Ms MacLaren said.

"It was 37 police, then the protectors of the wetlands saw them and went 'what is going on here' and then they saw there was someone drilling."

Ms MacLaren said when word got out about the number of police officers present, more people opposed to the extension went down to the protest area to support those already there.

"Sixty people were eventually pulled down into this area that was really created because of the police presence."

No arrests were made, though several move-on notices were issued to protesters.

Police Minister rejects police numbers over-the-top

Police Minister Liza Harvey earlier rejected claims the attendance of so many officers had been over-the-top, saying that was a decision of the Commissioner but she was supportive.

"People are allowed to protest in this State, but if they break the law we resource police to deal with that," she said.

"Had things gone pear-shaped at Roe 8, the police would have been there to intervene."