A teenage girl has been arrested on suspicion of attempted murder after two teachers and a pupil were stabbed at a school in south-west Wales.

Dyfed-Powys police said the injuries were not life-threatening and officers were continuing to investigate the incident after they were called to Ysgol Dyffryn Aman in Carmarthenshire at 11.20am on Wednesday.

Supt Ross Evans, the Carmarthenshire commander, said: “Emergency services immediately attended and the school was locked down for the safety of all on the premises. Three people – two teachers and a teenage pupil – have been taken to hospital with stab wounds.

“The family members of all those injured have been informed. A teenage girl has been arrested on suspicion of attempted murder and currently remains in police custody. A knife has been recovered in evidence.”

Evans said police were working with the school and other agencies to ensure support was available after the “very distressing incident”. He asked that people stop circulating footage of the incident on social media to avoid contempt of court and causing further distress. He added that officers would be in the area in the coming days.

By Wednesday evening, only a few police vehicles remained behind the school gates as calm descended on the small former mining town.

One mother of two children at the school who arrived at the neighbouring leisure centre said they were “shaken” by the day but saw and heard very little other than the “gossip” of schoolmates.

“They know that two teachers were hurt, there’s speculation as to who did what to who,” she said. “We’re just relieved it wasn’t them who were hurt … You would never expect something like this to happen here.”

The school’s headteacher said he was “proud” of students’ response to the incident. In a statement posted on the school website, James Durbridge said: “Today has been a very difficult day for us all in the school. It goes without saying that my thoughts are with the three individuals and their families, who have been affected by today’s incident.

“I wish to commend all staff and pupils for their calm and mature response during today’s lockdown. We are proud to have witnessed pupils embodying the school’s core values while supporting their peers and staff.”

The BBC named one of the injured teachers as Fiona Elias, the head of year seven.

Ysgol Dyffryn Aman, which translates as Amman Valley school, would remain closed on Thursday to allow police to carry out investigations, said Darren Price, the leader of Carmarthenshire county council. Praising the school’s response to the “shocking incident”, he said wellbeing support would be available for pupils, parents and staff, and that lessons would be moved online.

Emergency services were at the scene throughout Wednesday. The Welsh ambulance service sent four emergency ambulances and a hazardous area response team to the scene. Air ambulance helicopters also attended.

The school released pupils at 3.20pm, where they were hugged by tearful parents who had gathered to wait for them.

The first minister of Wales, Vaughan Gething, said on X that he was shocked by the incident. “A deeply worrying time for the school, families and community. Diolch [thank you] to first responders,” he added.

The UK prime minister, Rishi Sunak, said he was “shocked” at the news, while the home secretary, James Cleverly, praised police and medical services for “acting so promptly” and asserted that the school system and life in the UK were “very safe”. Jonathan Edwards, the independent MP for Carmarthen East and Dinefwr, said the incident was a “huge shock” and he could not recall anything like it happening in Wales before.

Adam Price, the Plaid Cymru MS for Carmarthen East and Dinefwr, who attended the school, said it was “an excellent school in a really close-knit community”. He said there would be lessons to learn from the incident to “minimise – as far as is ever humanly possible – the chances of this ever happening again in Ammanford, or any other community in Wales”.

Social media posts sent from the scene showed a heavy police presence as well as a large number of people waiting outside the school gates. Further footage showed air ambulance helicopters taking off from the school grounds.

One parent, Charlotte Rogers, who was waiting for her daughter to leave the school, said: “She said she was scared. She’s a tough cookie, so fingers crossed. I just want to give her a big hug. I just want everyone to be safe. This shouldn’t have happened. At the end of the day, they should have had measures in place beforehand, when they first opened the school, to make sure it was safe for them.”

Ysgol Dyffryn Aman is a bilingual and mixed-gender comprehensive school with about 2,000 pupils. It is known for the sporting prowess of its alumni, who include the former Welsh rugby international Shane Williams, the England rugby player Harry Randall and the Wales rugby captains Hannah Jones and Jac Morgan.

Dyfed-Powys police said they were not looking for anyone else in connection with the incident. Anyone with information that could help officers with their investigation is asked to report it to Dyfed-Powys police through a dedicated public portal.