At least 17 people are dead in yet another horrific school shooting in the US after a teenage gunman opened fire on Marjory Stoneman Douglas high school in Parkland, Florida, with an AR-15 assault rifle.

The suspect has been named as 19-year-old Nikolas Cruz, a former pupil who was expelled from the school. It is the 18th school shooting incident in 2018 alone and the deadliest since 26 people were killed at Sandy Hook school in 2012.

Three were shot dead outside the school when the attack began at 14.30 local time (19.30GMT) before the attacker went inside the building and killed another 12, Broward County Sheriff Scott Israel told reporters. Another two later died in hospital. Some victims are still being identified and three people remain in a critical condition while three others are in stable condition.

'It's catastrophic. There really are no words,' Sheriff Israel tweeted later.

President Trump offered his 'prayers and condolences' and tweeted that 'no child, teacher or anyone else should ever feel unsafe in an American school'.

Evangelical leaders also expressed their horror in the aftermath of the shooting. Out of Trump's primary evangelical advisers, no one raised the question of whether tighter gun laws might have prevented the attack.

Paula White, who pastors New Destiny Christian Center in Apopka, Florida, and is Trump's closest spiritual adviser, said it was 'horrifying' to see another school shooting.

'As a mother and a grandmother, I grieve for the victims who have had their lives and futures stolen from them, and for the families who are left to cope with the aftermath of this terrible tragedy,' she said in a statement. 'We pray that God would be close to the brokenhearted, as He promises us in scripture He will be, and that the community of Parkland will be comforted in their time of need.'

Dr Ronnie Floyd, president of the National Day of Prayer Task Force, said America must 'call on the Lord' in response.

'Let us pray for the victims of this terrible attack and their families the way we would like others to pray for us,' he said in a statement. 'It's in times like these when we need God's presence and comfort the most. May God be with all of us and our nation.'

Rev Samuel Rodriguez, President of the National Hispanic Christian Leadership Conference, said he was 'heartbroken and deeply troubled' for America in the wake of the attack.

'Let every American stop what he or she is doing, and call out to God on behalf of all of America's students, that God would spare our nation of ever again having to mourn such a senseless loss of life at our children's schools,' he said.

The attack is the 18th on or around school premises so far in 2018 alone, according to research by by Everytown for Gun Safety, and the sixth school shooting incident in 2018 that has either wounded or killed students.

One student, Bailey Vosberg, said: 'I heard what sounded like fireworks and I looked at my friend and he asked me if I heard that.'

He added, according to the BBC: 'Immediately, I knew. I didn't say anything to him, I just hopped over the fence and I went straight to the road that our school is located on – and as I got there there was just Swat cars and police units, police vehicles just flying by, helicopters over the top of us.'