A baby boy has died in suspicious circumstances in NSW's Hunter region over the weekend.

NSW Police say the seven-month-old boy was taken to Muswellbrook Hospital in an "unresponsive state" on Sunday afternoon.

"Despite the efforts of hospital staff, the baby was unable to be revived," police said in a statement on Monday.

A crime scene has now been set up at a Hunter home which is being examined by specialist forensic officers.

A post-mortem examination will be conducted to establish the cause of death, which detectives are treating as suspicious.

AAP