A new high-speed road cutting through one of Perth's most environmentally significant conservation parks has been labelled a "death trap" after a spike in the number of drivers colliding with native animals.

Key points: Whiteman Park is one of Perth's most significant conservation parks

Whiteman Park is one of Perth's most significant conservation parks A road through it has been expanded to four lanes with high speed limits

A road through it has been expanded to four lanes with high speed limits A lack of fencing has seen a big rise in the number of animals hit on the road

Swan Valley wildlife carer Andrea Marzi said more than 30 kangaroos had been killed on New Lord Street since it opened as a four-lane 80-kilometres-per-hour link through Whiteman Park last Thursday.

"They've been rolled, hit, maimed — some have been left in a really, really bad state," she said.

Ms Marzi has been on site every night and morning attending to injured and dead animals, and warning motorists to slow down.

Andrea Marzi has been working around the clock to prevent cars from hitting kangaroos. ( ABC News: Gian De Poloni )

She said a lack of fencing sealing off the busy road from Whiteman Park allowed kangaroos and other wildlife to roam freely across traffic.

"It's sad — it really upsets my day," she said.

"But it's better knowing that I've got those roos across the road and there's no humans hurt than coming out here later in the day and finding roos crawling like I've been doing this week.

"Some have no legs, just smashed up to their hips crawling. It's horrible.

"If they're small I'll pick them up and take them to the vets, but if they're large sadly we have to shoot them because they're too big too move."

New Lord Street is a busy rural highway linking Ellenbrook with Beechboro. ( ABC News: Gian De Poloni )

A risk to animals and drivers

Ms Marzi said the road was extremely hazardous for drivers.

"I've seen the damage the roos can do to the cars, they can push them right back," she said.

"I saw one not so long ago on Lord Street that smashed his front right back.

"If there's a toddler in that car or if there's a kid in the front seat someone is going to get hurt, especially with some of our big boomers."

Kangaroos feed in a paddock on the eastern side of Whiteman Park. ( ABC News: Gian De Poloni )

Main Roads WA said in a statement there had been a much higher than expected impact on kangaroos since the new road opened to traffic.

A spokesman said a fauna fence would be installed along the east side of the new road in the coming two weeks.

The agency said speed reductions down to 60kph had been put in place in the meantime, as well as flashing message boards warning drivers of wildlife.

It also said it would monitor the movements of kangaroos and consider installing another fence on the western side of the road if necessary.

The lack of fencing around Whiteman Park allows kangaroos to freely cross four lanes of traffic. ( ABC News: Gian De Poloni )

'Slow down and be careful'

Ms Marzi said a lack of streetlights along New Lord Street was compounding the problem.

"Up to about quarter to six in the morning, you actually can't see this road it's so dark," she said.

"We definitely need fences. We also need our drivers to be aware and slow down, and we need some more lights.

"Please, if somebody slows down in front of you, don't speed past them because that's where the roo will end up.

"Just be careful."