Hero staffer wounds US school shooter, stops potential massacre

A potential school shooting in Illinois was thwarted on Wednesday (local time), after a school resource officer shot and wounded a former student who opened fire. 

Mark Dallas, the resource officer at Dixon High School, about 160km west of Chicago, was shot at by Matthew Milby, 19, at around 8am, according to reports.

He then returned fire, injuring the former student enough to prevent a potential massacre. 

The suspect was taken to hospital and is receiving medical treatment, police chief Steven Howell said during a press conference.

He explained that the school officer's "heroic actions" saved "countless lives". 

"I could not be more proud of the police officer and the way he responded to the situation," Mr Howell said. 

It's believed the shooter acted alone, Dixon City Manager Danny Langloss said, and there are no further threats to the safety of students at the school. 

"A lot of things went right today and many things could have gone wrong," Dixon Mayor Liandro Arellano Jr told reporters. 

Milby has been charged with aggravated discharge of a firearm, aggravated discharge at a school employee and aggravated discharge at a school building, Illinois State Police announced late Wednesday.