The devastated mother of a 14-year-old girl killed in the Florida high mass shooting has unleashed on President Donald Trump, screaming for him to do something to prevent another massacre.

'President Trump, please do something! Do something. Action! We need it now! These kids need safety now,' a grieving Lori Alhadeff begged during a live CNN broadcast on Thursday.

As tears streamed down her face, Alhadeff told of how her daughter Alyssa was among the 17 shot dead at Marjory Stoneman Douglas High School on Wednesday.

Lori Alhadeff, whose 14-year-old daughter Alyssa was killed in the Florida high shooting, unleashed on President Trump on Thursday, screaming for him to prevent another massacre

She glared into the cameras as she furiously demanded answers and urged Trump to take action on gun control.

Alyssa was among the 17 shot dead at Marjory Stoneman Douglas High School on Wednesday

'How do we allow a gunman to come into our children's school? How do they get through security? What security is there?' she yelled.

'The gunman - a crazy person - just walks right into the school, knocks down the window of my child's door and starts shooting. Shooting her! And killing her!

'I just spent the last two hours putting together the burial arrangements for my daughter's funeral, who is 14.

'President Trump, you say what can you do? You can stop the guns from getting into these children's hands. What can you do? You can do a lot! This is not fair to our families and our children to go to school and have to get killed!'

Her fury has been felt by the entire Marjory Stoneman community as teachers and students directly impacted by the tragedy also called from Trump to take action.

Angry students have also taken to social media demanding Trump do more than just offer 'prayers and condolences'

Trump on Thursday addressed the nation, saying he was making plans to visit the grieving.

He also said he would 'tackle the difficult issue of mental health,' but did not touch on the gun control debate.

Two Marjory Stoneman teachers issued emotional pleas to Trump during televised interviews following his press conference, with one going as far as saying she wasn't looking forward to his visit.

'To be quite honest, I don't really care that the president visits. Because the president is one that believes that we should have the right to bear arms,' teacher Alicia Blonde told Fox News.

'That it's okay for somebody to have a weapon that could kill 40 or 50 people in a matter of seconds. So, I don't agree with my president, with all due respect. He's my president. He was elected by the people but I disagree with my president.

Teacher Alicia Blonde said she wasn't looking forward to Trump's visit because 'the president is one that believes that we should have the right to bear arms'

Melissa Falkowski, who is also a teacher at Marjory Stoneman, broke down during an interview, saying it was time for Trump and Congress to do something

'I tell you right here, right now, that as a teacher and that as a citizen of this country, I will do everything I can to change these laws.'

Melissa Falkowski, who is also a teacher at Marjory Stoneman, broke down during an interview, saying it was time for Trump and Congress to do something.

She had earlier told of how she had helped 19 students squeeze into a closet with her.

'We were in there for probably 40 minutes. We were locked in the closet until SWAT came and got us,' she said.

Angry students have also taken to social media threatening to boycott Trump's visit and they demanded the President do more than just offer 'prayers and condolences'.

It come as the Moms Demand Action went to the Capitol on Thursday with 5,000 petitions to demand change to gun laws.

Nineteen-year-old Nikolas Cruz is accused of opening fire Wednesday at Marjory Stoneman Douglas High School in Parkland, killing 17 people. A judge Thursday afternoon ordered him to be held without bond on 17 counts of murder.

Nikolas Cruz, 19, is accused of opening fire Wednesday at Marjory Stoneman Douglas High School in Florida, killing 17 people

Staff and students walked single file outside the school as they evacuated after the shooting