Police are seeking public assistance to locate two children missing in separate incidents around Brisbane.

A 12-year-old girl last seen in a yard in Ellen Grove in the city's south-west this afternoon has been reported missing.

Meanwhile, an 11-year-old boy missing in the Virginia area on the northside of Brisbane has not been seen since Tuesday, November 25.

Queensland Police Service said they held concerns for both their welfares, describing the behaviour "out of character" for both.

A 11-year-old was last seen in Virgina on November 25. ( Supplied: Queensland Police Service )

The girl, described as being south-east Asian in appearance, about 165cms tall with a slim build and black hair, was last seen wearing a blue school uniform with yellow trim.

She was last seen on Julie Road in Ellen Grove about 5:15pm (AEST) on Friday but has not been seen since.

The boy was described as being Caucasian in appearance, about 145cms tall, of a solid build and has short light brown hair.

He was last seen wearing a black t-shirt and blue shorts and he has a green scooter.