Police are upping patrols in Buxton after what officers have described as a 'serious assault' in the town.
A 16-year-old boy was injured in the assault, which happened in the Marlborough Road area at around 9.20pm on Thursday.
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The victim was taken to hospital in Manchester for treatment and is in a stable condition.
Reports on Facebook say the assualt was a 'stabbing' - but police have not confirmed this.
A Derbyshire Constabulary spokesperson said: "We have a team of detectives working on the investigation and three people - a 42-year-old man and two youths aged 16 and 18 - remain in custody for questioning.
"Although we believe the incident to be isolated, we know that people living in the area might be alarmed by it.
"That's why we will be carrying out extra high visibility patrols throughout Buxton over the weekend.
"We're also there so that anyone who wants to come up and speak to us about this incident can do so.
"Anyone who witnessed the assault or has information that could help our investigation should call us on 101 and quote incident 1357 of May 30.
"You can also call Crimestoppers and leave information anonymously, on 0800 555 111."