Police have released a comfit image of a woman they believe has approached children and offered them lifts to school across Brisbane's south twice in the past week.

The first instance happened last Monday when the woman drove up to two teenagers, aged 15 and 17, as they walked along Pine Street at Runcorn about 8am.

Comfit of the woman police say has approached students in the South Brisbane area. Credit:Queensland Police Service.

She told them she was a teacher at their school and asked them if they wanted a lift, police said.

The pair refused and the woman drove off in her silver SUV.