Call that sparked police hunt was hoax

• NEW: Police are speaking to two 10-year-old girls about the hoax, they say
• NEW: Police spent 30 hours on the case and set up a special hotline
• NEW: The detective in charge of the operation calls it "incredibly frustrating"
• The caller phoned for an ambulance and said her mother had collapsed

London (CNN) -- A call to police in England that sparked a frantic search for a 3-year-old girl who said her mother had collapsed was a hoax, police said after spending nearly 30 hours trying to trace the call.

Two 10-year-old girls were being questioned Tuesday, West Yorkshire police said after the urgent hunt in the city of Leeds.

Detective Chief Inspector Lisa Griffin, who led the search, called the incident "incredibly frustrating."

Earlier Tuesday, the police force had issued an appeal for help tracking down the child who called emergency services to say her mother had fallen down and was not moving.

She said she had shouted at her mother and shaken her, but she remained motionless on the kitchen floor with a piece of toast in her hand, police said in a release.

The girl said her name was Ellie. The call for an ambulance came at 10:53 Monday morning. Police announced just before 4:30 on Tuesday afternoon that the incident was a hoax.

The West Yorkshire force had put a team of officers on the case, set up a phone number for tips from the public and put out appeals on Twitter and through television interviews.

"We urgently need the public's help to identify exactly where Ellie and her mum are," Griffin had said in launching the appeal.

The hoax caller said her mother was named Stacey Hall but was able to give only part of her address -- the number 23 and that the street name had "Court" in it.

Police released the information, plus part of the audio recording of the 33-minute phone call, in hopes that someone would be able to identify her.

No phone number came up when the girl called emergency services, West Yorkshire police told CNN, leading them to believe that the call came from a prepaid cell phone.

CNN's Laura Smith-Spark contributed to this report.