The shooting broke out at the Allina Health Clinic in Buffalo, USA, during the early hours of the morning local time, according to the local news site Star Tribune.
Several people are said to be seriously injured and one man has been arrested, the site writes.
Kelly Prestidge, an employee of the Buffalo police, tells the AP that it is unclear whether the detainee is the shooter.
Initially, information came that a bomb had detonated inside the clinic about 30 minutes after the shooting, but Kevin Smith, a spokesman for the FBI, told the AP that the information has not been confirmed.