A teacher and teenaged student have been shot and killed at a private Christian school in the US state of Wisconsin. 

At least six others were injured in the attack at Abundant Life Christian School in the city of Madison on Monday. Two of the injured sustained life-threatening injuries and are in a critical but stable condition in hospital. 

The shooter was identified by police as Natalie Rupnow, 15, who also goes by the name 'Samantha'.

Police said she was in attendance at the school before opening fire in a study hall with mixed grade students at the school. She is then reported to have turned the gun on herself and died on the way to hospital. 

Police are still working to establish a motive. They have not confirmed that Rupnow is linked to a manifesto allegedly by her that is circulating online.

The attack happened just days before the school was due to close for the Christmas break. 

Heartbroken locals gathered later on Monday to mourn and pray at a vigil at Blackhawk Church. 

Speaking to reporters on Monday night, Madison Police Chief Shon Barnes said, "Today is a sad day not only for Madison, for our entire country. We have to do a better job in our community."

Mr Barnes said that to the best of his knowledge at the time, police had not had any prior interactions with Rupnow. 

The school has asked for prayers. 

"All of our students have been united with their parents and we are grateful for all the support," it said in a post on Facebook. 

"We have been flooded with thoughts and prayers. This great nation is behind us. So grateful for the tsunami of prayers for our students, staff, and families."