An unofficial search is underway for the owner of a pet dog who accidentally boarded a Sydney bus on Tuesday and ended up in a different area.

Athena, a three-year-old American Staffordshire Terrier, got on the bus in Sans Souci, 17km south of the city center.

Katerina Hatzi told 9news.com.au her brother, Nik, was the one who realized the dog was lost when he saw her on the 476 bus yesterday.

The dog reportedly boarded at the stop near Weeney Street on Rocky Point Road.

“After three stops [he] heard someone calling out ‘whose dog is this,’ and [he] realized nobody owned the dog,” Katerina said.

Nik took a picture, which he sent to his sister to share on the local Sans Souci community Facebook page.

“We know how great this page is for lost pets or anything really.”

Nik kept an eye on Athena on the bus until she disembarked at Kogarah station, about 5km north of where she hopped on.

He followed her off the bus and, with the help of another commuter, made sure Athena didn’t get too close to the edge of the train platforms.

Then they took her to station staff, who took over from there.

A guard from Kogarah train station contacted Sydney Dogs and Cats Home (SDCH) in Strathfield, which took Athena in for the night.

At the time of writing, she is still at the shelter and her owner has yet to come forward.

“There has been so many reposts on Facebook but seems to be no word of the owner yet,” Hatzi said.