A man is in hospital with serious injuries after being bitten by three dogs while jogging in Sydney's southwest.


A police spokeswoman told AAP the 49-year-old was in the Miller area of Sydney's south-west on Sunday when the dogs attacked.


"A woman who witnessed the incident and rushed to give assistance to the man was also bitten. Our understanding is she suffered minor injuries," the spokeswoman said.


Paramedics took the man, who's in a serious condition, to Liverpool Hospital.


The police spokeswoman said the dogs were secured before being delivered to council rangers.


She said it was too early to tell how they got loose.


The breed of dogs involved in the attack have yet to be identified.


AAP