A 14-year-old schoolgirl has been seriously injured after a substance, believed to be acidic, was thrown at her outside her school in west London, along with another teenager and a staff member.

The girl remains in hospital with potentially life-changing injuries following the incident at Westminster Academy, Westbourne Park, which took place after school hours on Monday afternoon.

The Metropolitan Police said: “Urgent inquiries are under way to identify and arrest those responsible.”

A boy aged 16 remains in hospital with non life-changing injuries, and the staff member, a woman aged 27, has been sent home from hospital after also being hurt in the attack.

Westminster Academy said the teenage boy injured was a member of the public.

Two police officers were also taken to hospital by London Ambulance Service as a precaution after they reported feeling unwell.

Met Police officers attended the incident after being flagged down while on patrol on Alfred Road by a school employee at about 16:40 BST.

Two crews and hazardous materials specialists from London Fire Brigade were also sent to the scene to make it safe.

A Met police spokesperson said: “Tests of the substance are ongoing. At this stage officers believe it to be acidic.”

The school is closed, with lessons are taking place online and many staff working from home.

A Year 6 open morning was also cancelled.

Westminster Academy’s principal Numera Anwar said: “This was a distressing incident which took place after school hours when students and staff were leaving the school site.

“This is a difficult time for our community and I took the decision to close the school today to allow for a thorough investigation and to ensure the school can resume normally from tomorrow [Wednesday] with all safety measures in place,” Ms Anwar said.

“We are working with the local authority and will have counsellors and other support available onsite. The welfare of the students at Westminster Academy is always our priority and that continues to remain the case.”

She also warned against speculation into the nature of the incident.

“This will clearly be an unsettling time for the wider community and parents.

“While police lead the investigation into this incident I would urge everyone to avoid speculation as this will not be helpful and may compromise the investigation.”

A number of crime scenes remain in place as investigations are carried out, the Met says.

Adam Hug, leader of Westminster City Council, described the attack as “truly shocking” and said the local authority was assisting the school.

“The council has been in touch with Westminster Academy and we will provide educational psychologists and any other support to help children through what is a traumatic ordeal.

“Our thoughts are with all those who have been affected.”

He added: “Clearly this attack will be unsettling for the whole academy and the wider community, and we will be working with police to provide reassurance and whatever support we can.

“We would urge anyone with information about what has happened to contact the police.”