A murder investigation has been launched.
PC Andrew Harper, based at Abingdon Police Station, was attending a reported burglary in Berkshire.
The 28-year-old was only married four weeks ago.
Police said the incident happened last night at the crossroads of Ufton Lane and Lambdens Hill, near to Sulhamstead.
It's now been confirmed that there is a post mortem taking place at the moment - but officers know he was dragged along by a car at some point.
A scene watch remains in place.
Ten males, aged between 13 and 30, are being held on suspicion of murder at various police stations across the Thames Valley.
At a press conference on this afternoon, Chief Constable John Campbell said PC Harper was at the scene with a fellow officer and was out of his police car when the incident occurred, adding: "What we do know is Andrew had been dragged along by a vehicle."
He said the suspects were detained within about an hour of the incident and officers are working "hard and diligently to find out what happened".
Deputy Chief Constable Jason Hogg said: "Our deepest thoughts at this time are of course with Andrew’s friends and family, who are being supported by specially trained family liaison officers.
"Our thoughts also extend to all of Andrew’s colleagues within Thames Valley Police.
"As a force we are devastated at the loss of our colleague and will all be supporting each other at this difficult time."
Senior investigating officer Detective Chief Inspector Stuart Blaik, of the Thames Valley Police Major Crime Unit, said: "This is a tragic incident, and I would like to reassure the public as well as our officers and staff that we have launched a full and thorough investigation to establish what has happened."
Officers are also appealing for witnesses.
Meanwhile, tributes are pouring in online for PC Harper.
The Prime Minister, Boris Johnson, said the tragedy is a reminder of the dangers officers face:
My thoughts are with the family of PC Andrew Harper who was killed in the line of duty last night. https://t.co/YbvYCMBOrJ— Priti Patel MP (@patel4witham) August 16, 2019
Home secretary Priti Patel has sent her condolences to the officer's family.
Anthony Stansfeld PCC said: “I would like to offer my deepest condolences to the family, friends and colleagues of PC Andrew Harper. "
"This is a tragic loss for the force and I know that Thames Valley Police are doing all they can to support those who have been affected."
Very sad and shocking news. My thoughts are with PC Harper’s family, friends and colleagues https://t.co/jhLAcsfFZe— Ed Vaizey (@edvaizey) August 16, 2019
Sad news from last night for our emergency service colleagues at Thames Valley Police. Thoughts and condolences go out to the colleagues, friends and family of PC Andrew Harper @ThamesVP @tvprp #ThinBlueLine pic.twitter.com/ACyZcOSdNY— Thame Fire Station (@FireThame) August 16, 2019
Truly devastating news from @ThamesVP. Thoughts are with PC Harper’s family, friends and colleagues at this terrible time. I’ve spoken with colleagues from @TVPFED and with the @TVP_Chief to give my condolences and support. Such shocking news, so sad. #policefamily https://t.co/Z8RfYF6y6J— John Apter (@PFEW_Chair) August 16, 2019
More to follow