A baby kangaroo has been rescued after it was found inside a Gold Coast post office box this morning.

Queensland Fire and Emergency Service crews and Australia Post were called out to Stapylton Jacobs Well Road at Woongoolba just before 7:00am.

Michael Beatty from RSPCA Queensland said a complaint of cruelty was being investigated.

"Our inspectorate will be looking into the incident," he said.

"Honestly, you see some very strange things in this job but this defies belief really."

Joey 'obviously very stressed'

The joey has been taken to the Currumbin Wildlife Hospital for treatment.

The hospital said the eastern grey kangaroo is about seven months old and was dehydrated on admission, but X-rays and blood tests have come back normal.

The joey is expected to be placed with a Wildcare foster carer later today.

The RSPCA is appealing for anyone with information to come forward.

"It is a very young, small joey," Mr Beatty said.

"If anyone has any information just give us a call on 1300 ANIMAL."