Imani Green, 8, of Balham in south London, was standing inside a clapboard grocery store and bar with Jamaican relatives Friday evening when a gunman wearing a hoodie shot the child in the head and shoulder before also shooting and wounding three adult members of her family.
The high command of Jamaica's police force said Sunday that Imani was "mercilessly slaughtered in front of family members in a hail of bullets as gangsters sought to exact revenge on their rivals" in the normally quiet Red Dirt district of Duncans in Trelawny parish.
The roadside business where the shooting occurred is apparently owned by a female relative of the slain girl. There have been no arrests.
The girl died from her injuries while undergoing treatment at a hospital in nearby Falmouth, a historic coastal town that is home to the tourism-dependent Caribbean island's newest cruise ship port. The three adults were listed in stable condition.
The British Foreign & Commonwealth Office said it was providing consular assistance to the family and working with authorities in Jamaica.
James Mortimer, a press officer with the British agency, said Imani's relatives were "very distressed" and "appealing for privacy." Imani, her mother and sister had planned on visiting relatives in Jamaica until the end of the month.
Janella Parmer, the slain child's sister, told the BBC that she found her young sibling in a pool of blood after hearing gunshots outside.
"I picked her up off the ground and realized she was still breathing. I flagged down a car and they drove us to hospital. The rest is history," the BBC quoted Parmer as saying.
Jamaican Security Minister Peter Bunting said the "senseless killing of a young, innocent child must outrage all well-thinking Jamaicans."
The island's government said the Falmouth police are conducting an "extensive investigation into the matter and will expend every effort to ensure that the perpetrator is apprehended and brought to justice."
There has been a heavy police presence in Duncans since the shooting.
Neighbors said they were shocked by the slaying of the child in a generally peaceful district where many people farm for a living or commute to jobs in Falmouth or Montego Bay. Pastors decried the violence during weekend church services.
"It is so, so sad. And for this to happen in Duncans is just hard to believe. This is maybe the second shooting here that I can remember," said resident Elaine R. Duncan.
Sadiq Khan, a British lawmaker who represents the schoolgirl's south London area in the British Parliament, tweeted Sunday that he was "devastated" to learn of the killing.
There were 1,087 homicides last year on the island of some 2.8 million people. It was the lowest number of killings in nine years in Jamaica, but authorities acknowledge that the island's rate of violent crime is still unacceptably high.
Most of Jamaica's violence takes place in rough slums, with tourist resorts largely crime-free.