Police are contacting parents of children at the nursery
Police have arrested a 39-year-old nursery worker in Plymouth in connection with the distribution of indecent images of children.
It follows a raid on the woman's home and Little Ted's nursery in the city.
The nursery, which has about 60 children, has been closed while inquiries are carried out. The woman is being held in custody.
Internet crime investigators and children's care specialists are involved in the operation.
Items seized in raids included computer equipment which contained "dozens of internet images", according to police.
Ch Supt Jim Webster on the arrest of a 39-year-old nursery worker in Plymouth
Commanding officer Ch Supt Jim Webster said it had been a "fast-moving investigation" after allegations were made to police on Monday evening by someone outside the region who had received a number of images.
He said the allegations raised "serious concerns" and police were contacting all parents of children at the nursery.
He said: "We received information yesterday evening about nine o'clock, took it very seriously, had it researched straightaway and by midnight last night we'd arrested a person who we believe is concerned in the distribution of child pornography images.
"So our work today is to find out what's happened, where the images have come from, where they've been sent to and any risk to anybody in Plymouth."
Little Ted's opened in 1992 and operates from Laira Green Primary School and Laira United Church Hall.
Officers carried out a major search at the nursery
Children in the nursery are aged between two and five, but children up to 11 can attend the breakfast and after-school clubs.
People arriving at the nursery to drop off children on Monday morning were handed a letter by police explaining what had happened.
The letter, signed by Supt David Sumner, read: "We are informing you that police have arrested a 39-year-old woman in connection with distributing indecent images of young children and that the woman is an employee of Little Ted's Child Day Care Unit, Old Laira Road.
"As part of our inquiries we have searched the home address of the woman and need to search units one and two of the unit today."
Mother Amy Gilbert said: "It's a complete shock. I am going to change nurseries."
Parents affected can contact a special police helpline on 08452 777444.
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