A 15-metre-wide sinkhole that appeared overnight in the car park of a busy Perth shopping centre is getting worse, shop owners say.

The car park of the Stockland shopping centre in Baldivis was cordoned off about 6:30am on Saturday after reports of the bitumen collapsing.

No cars were parked in the area at the time and there were no customers present.

The shopping centre remains open, but customers are being encouraged to park elsewhere.

Shop owners and witnesses have been monitoring the sinkhole and believe it has worsened since this morning.

"It's definitely been sinking more and more," one shop owner told the ABC.

In a statement, Stockland said the car park would be closed until further notice.

"Stockland is undertaking a full investigation with engineers, working in conjunction with local authorities," the statement said.

"The southern part of the car park will be closed during the investigation and remedial works will be undertaken to rectify the issue.

"The safety of our customers and retailers remains our first priority."

The sinkhole appeared overnight. ( ABC News: Madeline Palmer )

Locals shocked at speed of growing sinkhole

Local Baldivis resident Julie Owen said she was concerned at how fast the sinkhole appeared and how it seems to be getting bigger by the hour.

"From all the comments posted on a local chat page, everyone seems to be quite shocked and astonished," she said.

"They're all coming to their own conclusions as to why it's happening, but nobody really knows yet why it's just occurred overnight."

The shopping centre car park was cordoned off early on Saturday morning. ( ABC News: Madeline Palmer )

Ms Owen said she had hoped the shopping centre would take proper safety precautions.

"It'd be nice for them to let us know what's going on, what the assessment found, what's causing the problem and are we all at risk."

"Because there's been no warning and apparently it's just business as usual.

"Without knowing what's going on underneath the ground, anything's possible."

Remedial work is being carried out on the car park. ( Facebook: Julie Owen )

City of Rockingham Mayor Barry Sammels said he only found out about the sinkhole through social media.

He said people should avoid the area.

"We are concerned for the safety of the community and we'd like to urge people to stay clear of that location," he said.