A school in south-west Wales has been locked down after three people were injured in an incident and one person was arrested, police have said.

Dyfed-Powys police said in a statement they were not looking for anyone else in connection with the incident at Amman Valley school in Ammanford.

Emergency services remained at the scene after being called shortly after 11.15am on Wednesday and the school closed while the investigations continued. Air Ambulance helicopters also attended.

The school released pupils from lockdown at 3.20pm, where they were greeted with tearful hugs from the parents who had gathered to wait for them.

Local reports said that the victims were injured by stabbing and that among those hurt was at least one member of staff.

The school said the family members of all injured people had been informed.

A statement on the Amman Valley School website said: “You will be aware of the incident that has taken place at Ysgol Dyffryn Aman today. The family members of all injured persons have been informed. We would like to reassure parents and the public that the incident has been contained.”

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, expressed shock. Sunak, who is in Berlin, Germany, posted on X: “Shocked at the news emerging from Ammanford today. I want to thank the police and emergency services for their ongoing response and my thoughts are with all those affected.”

The home secretary, James Cleverly, said his thoughts were with the people affected. Cleverly, who is in Lampedusa, southern Italy, posted on X: “I am being kept informed about the events in Ammanford, Wales. My thoughts are with the school and all those involved. I want to thank the police & emergency service for their ongoing response. It is important they are given the space to carry out their investigations.”

Dyfed-Powys police said in a statement: “Dyfed-Powys police is dealing with an incident at Amman Valley school. Three people have been injured and are receiving treatment. One person has been arrested and we are not looking for anyone else in connection with this incident. Emergency services remain at scene and the school has been closed while investigations continue.

“We are working closely with the school and Carmarthenshire county council. We are aware that there is footage of the incident currently circulating on social media. We would ask that this is removed to avoid contempt of court and distress to those affected. We would ask people, do not speculate while there is a police investigation ongoing.”

Welsh ambulance service said it was called shortly after 11.15am and sent four emergency ambulances and a hazardous area response team to the scene, where crews were supported by two Cymru high-acuity response unit paramedics and an operational manager.

Social media posts from the scene showed a heavy police presence as well as a large number of people waiting outside the school gates. Other footage showed the 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 that one teacher and two pupils had been stabbed, that’s all I know.

“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.”

Amman Valley school, also known as 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 Welsh rugby international Shane Williams, the English rugby international Harry Randall, and Hannah Jones and Jac Morgan, two captains of Wales rugby teams.

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