An off-duty police officer is in a critical but stable condition after being shot at a sports complex in Omagh, County Tyrone.
There are unconfirmed reports that he was hit multiple times on the Killyclogher Road at about 20:00 GMT.
The Police Federation for Northern Ireland said two gunmen were involved and he was shot while he coached young people playing football.
Rishi Sunak said he was “appalled by the disgraceful shooting”.
“There is no place in our society for those who seek to harm public servants protecting communities,” said the prime minister.
Police Service of Northern Ireland (PSNI) Chief Constable Simon Byrne said he was “shocked and saddened” by the events.
“We will relentlessly pursue those responsible,” he tweeted.
The victim is being treated at Altnagelvin Area Hospital in Londonderry.
At the scene: Michael Fitzpatrick, BBC News NI reporter
Police forensic officers are carrying out an examination of the grounds of the sports facility where the off-duty officer was shot.
Local politicians who arrived shortly after the gun attack say it was a chaotic scene as parents arrived to pick up children from training.
They say it was very busy this evening with a number of different sports groups using the facility.
The complex has been sealed off while police commence their investigation.
A number of cars remain in the car park, within the police cordon, with the entire complex now a crime scene.
The Northern Ireland Ambulance Service said it received a call about the shooting at Youth Sport Omagh at 20:00 GMT and sent a crew.
Sinn Féin deputy leader Michelle O’Neill said it was an “outrageous and shameful attack” and added: “I unreservedly condemn this reprehensible attempt to murder a police officer.”
Democratic Unionist leader Sir Jeffrey Donaldson condemned the “cowards responsible for this”.
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Former justice minister and Alliance leader Naomi Long said her thoughts were with those affected by this “evil act of cowardice”.
SDLP leader Colum Eastwood, MP, said it was a “chilling attack on an individual serving his community”.
Ulster Unionist assembly member Tom Elliott said it was a “despicable and cowardly action”.
The Northern Ireland Secretary, Chris Heaton-Harris, said that “those responsible for such horror must be brought to justice”.
Taoiseach (Irish PM) Leo Vardakar said he condemned the “grotesque act of attempted murder”.
The Irish Minister for Foreign Affairs, Micheál Martin, said he was “shocked and appalled” by the shooting.
This is probably the most serious attack on a police officer since the murder of Ronan Kerr in 2011.
That attack, like this, took place in Omagh.
The officer targeted is a detective of quite senior rank.
He has a public profile, having carried out media duties as the lead officer on several high-profile cases.
These cover both dissident republican violence and crime gang murders.
The police have said nothing officially about a potential motive for the shooting.
But among fellow officers, suspicion in the first instance has fallen on dissident groups.
Despite a relative lull in activity in recent years, the New IRA in particular has continued to target police officers.
The Police Federation for Northern Ireland said it “condemned this appalling and barbaric act of violence on an off-duty officer”.
“Our thoughts are with our colleague and his family. These gunmen offer nothing to society. Anyone with information should come forward.”
An Garda Síochána (Irish police) said it had intensified patrolling in border counties.
The last gun attack on a PSNI officer was in January 2017. The PSNI officer was hit by an automatic gunfire at a petrol station in north Belfast.
The officer was hit at least twice in his right arm, and it is thought a bulletproof vest may have saved his life.