Prosecutors have demanded the man charged with killing 17 students and teachers at a Florida high school last month face the death penalty.

Nikolas Cruz, 19, will reappear in court Wednesday local time facing 34-charges, including 17 counts of first-degree murder, over the Marjory Stoneman Douglas High School massacre.

The office of Broward County State Attorney Michael Satz filed the formal notice of its intentions Wednesday morning (AEDT) to seek his execution.

The notice cited multiple reasons under Florida law for the death penalty including the charges that Cruz “knowingly created a great risk of death” to many people, the shooting was “especially heinous, atrocious or cruel,” and it was committed in a “cold, calculated and premeditated manner”.

News of the proposed death penalty comes as a wounded student credited with saving the lives of 20 of his classmates is showing signs of improvement.

Fifteen-year-old Anthony Borges, who was shot while attempting to close and lock a classroom door during the attack, is the last of the shooting victims still in hospital.

Anthony fell critically ill of an intestinal infection last week, but hospital staff told local media Wednesday that his condition was upgraded to fair after several surgeries.

Cruz’s lawyers previously said the former student would plead guilty only if the death penalty was not pursued by state prosecutors.

The action by prosecutors does not necessarily mean a plea deal will not be reached, the Associated Press reported.

Cruz’s only other penalty option is life in prison with no possibility of parole.

Broward County Public Defender Howard Finkelstein, whose office is representing Cruz, has said there were so many warning signs that Cruz was mentally unstable and potentially violent, and that the death penalty might be going too far.

Mr Finkelstein said Cruz would likely plead guilty if prosecutors not seek the death penalty. 

Anthony Borges is the last remaining shooting victim in hospital. Photo: Twitter

“Because that’s what this case is about. Not, did he do it? Not, should he go free? Should he live or should he die,” Mr Finkelstein told AP last month.

Anthony Borges, was shot five times as he blocked his classroom door against Cruz.

The Borges family lawyer, Alex Arreaza, said Anthony’s intestinal area had been sealed off and he was breathing on his own after being taken off a ventilator.

The Borges’ family has filed notice that they will sue Florida authorities to seek money to cover the cost of his recovery.

-with agencies