Man assaulted and tied up in Sydney home invasion

A man's been assaulted and tied up in his bathroom during a home invasion in Sydney's south.

Just after midnight a man and woman armed with a knife broke into the granny flat of a home at Penshurst.

The pair assaulted the 24-year-old and dragged him to the bathroom where he was tied up, police said.

They rummaged through the flat and left a short time later.

The 24-year-old managed to free himself and call police.

He was treated at St George Hospital for soreness and bruising to his face and body.

Police say the assailant was Caucasian, about 30 years-old with dark hair and had a tattoo on his right calf.

The woman is described as 30 years-old, with a medium build and shoulder-length blonde hair.

-AAP