Reese Witherspoon has been left ''heartbroken'' after 17 people were killed in a shooting at a school in Florida.

The 'Big Little Lies' actress has urged for people to ''do more'' to prevent such shocking attacks after 19-year-old Nikolas Cruz returned to Marjory Stoneman Douglas High School in Parkland, Florida - from where he'd previously been expelled - with a firearm, the 18th gun-related incident in a US school this year.

She tweeted: ''Heartbroken over the news of another school shooting. This is the 18th in 45 days of 2018. Students & teachers shouldn't have to fear for their safety. We must do more to prevent these senseless acts of gun violence. My heart is w/ the people in Parkland, FL. Enough is enough (sic)''

Her comments were echoed by Kim Kardashian West, who has been a firm supporter of stricter firearm legislation, especially since she herself was robbed at gunpoint in October 2016.

She posted: ''We owe it to our children and our teachers to keep them safe while at school. Prayers won't do this: action will. Congress, please do your job and protect Americans from senseless gun violence.''

Ellen Degeneres, Mark Ruffalo and Chelsea Handler also called for stricter action.

Ellen posted: ''No words, no actions, no laws are enough until we end this epidemic of school shootings in our country. My heart is with the students and parents of Marjory Stoneman Douglas High School.''

Mark tweeted: ''Prayers without accordant action are silent lies told to oneself, heard by no God, amounting to nothing. Action is the language of truth, the prayers of the Saints.''

And in a damning tweet, Chelsea wrote: ''We have to elect candidates that are not funded by the NRA in November. We have an opportunity to elect candidates who won't allow kids to go to school and get shot. It is disgusting how many times this has happened and Republicans do nothing. You all have blood on your hands.''

Britney Spears reached out to offer her condolences to those affected by the tragedy.

She wrote: ''Just heard the tragic news about Florida. My heart breaks for the students of Marjory Stoneman Douglas High School. Keeping the victims and their families in my thoughts #PrayForParkland (sic)''

Broward County Sheriff Scott Israel said 12 people had been killed within the school building, two people were killed just outside, one on a nearby street corner and two people died in hospital.

Three people remain in a critical condition and three others are said to be stable.