A police officer has been killed while attending a reported burglary.
PC Andrew Harper, of Thames Valley Police, died at about 23:30 BST on Thursday in Berkshire.
Ten people aged between 13 and 30 have been arrested on suspicion of murder and are in custody at stations across the area.
Prime Minister Boris Johnson tweeted that he was “deeply shocked and appalled” by the officer’s death.
The force said PC Harper, who was from the Roads Policing Unit based in Abingdon, was killed while performing his duties.
A cordon has been put in place at the scene near the A4 Bath Road between Reading and Newbury, at the crossroads near to Sulhamstead.
Mr Johnson said PC Harper’s death was “the most powerful reminder that police officers up and down the country put themselves at risk every single day to keep us safe”.
“My thoughts are with PC Harper’s family, friends and colleagues at this terrible time,” he added.
Deputy Chief Constable Jason Hogg said: “As a force we are devastated at the loss of our colleague and will all be supporting each other at this difficult time.”
Andy Fiddler, from the Thames Valley Police Federation, said: “This is totally devastating news.
“All our thoughts – and the thoughts of the entire police family across the UK – are with the family, friends and close colleagues of PC Andrew Harper who died last night.”
The Independent Office for Police Conduct said it had been made aware of the death because of possible issues around a police pursuit.
Home Secretary Priti Patel tweeted her thoughts were also with the officer’s family.
Senior investigating officer Det Ch Insp Stuart Blaik said it was “a tragic incident”, adding: “We have made a total of 10 arrests in connection with this incident, and those arrested are currently in police custody.
“Those arrested are all male and aged between 13 and 30.”
The attack on PC Harper is the third time in recent weeks an officer has been hurt in the line of duty.
Metropolitan police constable Stuart Outten was stabbed in the head on 8 August.
Days later a 42-year-old West Midlands police officer suffered serious head and pelvic injuries when he was run over with his own vehicle.