LONDON -- The text message from a young boy, writing in broken English on a no-frills cellphone, was frightening enough to set off a frantic, trans-Atlantic search that saved the lives of 15 migrants trapped in a locked truck in England.

The message flashed on the cellphone of volunteer Liz Clegg, who was attending a conference in New York: "I ned halp darivar no stap car no oksijan in the car no signal iam in the cantenar. Iam no jokan valla." It was written by Ahmed, an Afghan boy of about 7, trying to say: "I need help. The driver won't stop the car. No oxygen in the car. No signal. I'm in a container. I am not joking. I swear to God."

In March, Clegg and others volunteering at a squalid migrant camp in Calais, France, had handed out hundreds of basic cellphones to children living there, programming in a number for them to text in a crisis.

She knew Ahmed wouldn't text something like that if he wasn't in danger. So she called Tanya Freedman, from the Help Refugees charity in London, to tell her the boy seemed to be suffocating.

Freedman called police in southeast England to tell them of the emergency. The police response was swift and effective, she said.

"I conveyed to them that it was a life-and-death situation," Freedman told The Associated Press on Friday. "I had Ahmed's number and the first thing they did was find an interpreter who spoke Pashto to talk to him. They called him and immediately they realized it was an emergency, and they were able to put a trace of his cellphone and find out he was in a lorry (truck) in Leicestershire."

Kent Police said in a statement they received a call at 2:50 p.m. Thursday reporting that migrants were believed to be in danger in a truck, and that police established the truck was in Leicestershire. The information was given to police in Leicestershire, who quickly found the truck parked at a highway service station, broke into the back and freed 15 oxygen-starved migrants.

Only then did Freedman exhale: "It was absolutely nerve-wracking waiting to see if the police could find this boy in time to save his life," she said.

Leicestershire Police said 14 migrants were detained on suspicion of entering Britain illegally, with their cases to be handled by immigration officials, and one man was arrested on suspicion of illegal trafficking.

Police said one child was placed in protective care. None involved gave his last name because he is a minor.

"I think it's extraordinary that a 7-year-old boy knew his life was in danger and had the presence of mind to know what to do and give the right information and save himself and the others in the truck," Freedman said. "We hope he's getting the right kind of care."