An arrest warrant has been issued for a south-western Sydney woman who is believed to have abducted her young son.

Police say Tamara Jankovic took her six-year-old son Matthew Papalia from a relative's home against court orders.

The 29-year-old allegedly took the boy from a house at Liverpool on January 13 and is believed to have flown to Brisbane.

Police say the pair was last seen in Queensland's Southport after they boarded a flight to the Gold Coast that evening.

Detective Inspector Dean Johnston from Liverpool Police Station is urging the public to keep a look out.

He says police are worried about Matthew's welfare because he has a medical condition.

"It appears that all our avenues of investigation have now been exhausted," he said.

"We are now urging the community, particularly those in the south eastern region of Queensland to provide information to ensure the location of Matthew and his well being. We also urge Tamara to come forward to ensure the wellbeing of her son.

"Matthew is described as being Caucasian in appearance about 105 centimetres tall. Thin build, fair complexion, with brown hair and brown eyes."

Matthew Papalia. ( NSW Police )

Police believe the mother and son are still in Queensland and are working with their interstate counterparts to find the pair.

Ms Jankovic is described as being blonde with blue eyes, between 170cm and 175cm tall, with a medium build.

Matthew Papalia is a ward of the state.

Anyone who sees the pair is urged to call triple-0.