On Friday morning, as the final classes of the week were under way, panicked students began streaming out of a prestigious school just outside Bangkok.

Inside, police say, a 14-year-old boy had opened fire at the Debsirin School in Nonthaburi, on the outskirts of the Thai capital.

"I was standing in front of the teacher when she was shot," a shaken seventh grader tells the BBC, near the school gates. "She was talking to me when (the gunman) showed up."

Still in her uniform, with her mother by her side, she explains how the shooter stalked from room to room.

Police say he killed five teachers and injured more than a dozen people - including pupils - before turning the weapon on himself. Earlier, he had gunned down his grandparents.

"I had to climb over the school fence to escape with other friends," the girl - who the BBC is not naming - continues.

Her mother says the girl thought she might die. "[She said] 'I thought I'd never see you again'."

Metres from the school gates, paramedics loaded the wounded into ambulances and rushed them to hospital, as milling crowds hugged and cried.

One 18-year-old student told Reuters he initially thought there were firecrackers going off.

"I didn't think it was a gun at first," he said. "There were many shots: bang bang bang. Then it went quiet. Then it started again."

This is Thailand's deadliest mass shooting in years - and the second at a school this year.

In February, a head teacher and a female student were shot by an 18-year-old gunman during a school siege in southern Thailand.

Four years ago, a 34-year-old resident in the eastern Nong Bua Lamphu province killed 37 people, most of them preschoolers, in a shooting and stabbing at a nursery.

These crimes have resurfaced questions about gun control in the country.

While there are restrictions on gun ownership in Thailand, people can still acquire guns - legally or illegally - with relative ease.

Thailand has one of the highest rates of gun ownership in South East Asia - and it's not clear if authorities have taken any significant action to curb gun crime amid rising concerns.

"This shouldn't have happened," the boyfriend of one of the killed teachers told reporters, clearly distressed and trying to hold back tears.

It is early days in the investigation and police haven't said anything about a motive.

They have said they believe the 9mm handgun the shooter used belongs to his grandfather, who was a teacher, but little else.

Others are filling some of the gaps. A teacher at the school has said the shooter was a good student - not aggressive and with good grades - and education authorities have described him as an avid gamer.

But it is clear authorities will have many questions to answer in the coming days - many of them about what change this crime must trigger.

An opposition leader has called for Thai authorities to review the country's gun control measures.

"An act of violence in an educational institution, which should be one of the safest places in our society, serves as a stark reminder for Thai society to seriously and systematically review gun control measures," Natthaphong Ruengpanyawut, leader of the People's Party wrote in a Facebook post following the shooting.