A thief masquerading as a good Samaritan offered to help a woman after a car crash before stealing her credit cards, police allege.

A 57-year-old woman was distressed and in shock after the crash at Carlisle in Perth about 8am on Wednesday when the thief struck, Western Australia Police said.

A 32-year-old woman approached her to offer help, and the distressed woman handed her phone to the apparent good Samaritan to call emergency services on her behalf.

The phone’s case contained the 57-year-old’s credit cards and Medicare card, which the 32-year-old allegedly took with her when she left the crash scene before police arrived.

Kensington Police found the Medicare card in a drain near the crash site at the corner of Harris and Briggs streets.

They later tracked the woman down with the public’s help, police said on Saturday, and charged her with stealing.

The Redcliffe woman was due to front Perth Magistrates Court on Saturday.

-AAP