Police say the incident was a domestic situation.
Austin police and fire are responding to the scene of the shooting in the 9600 block of Great Hills Trail.
Around 2:30 p.m., the police said the suspect was still at large and asked residents to shelter in place.
“It appears this is a domestic situation that is isolated and there is no risk to the general public,” the police tweeted.
Austin-Travis County EMS said three adults were pronounced dead on scene.
No additional patients had been transported as of 2 p.m. and 18 units were on the scene, EMS said.
This is a developing story. Please check back for updates.