It's 9.01pm in Bangor. Do you know where your children are? (If not, they might be locked up)

It is late afternoon in Bangor, North Wales, and a group of seven teenagers is wandering down to the city centre. Spared lessons because of a teacher- training day, they have have been doing what young people tend to do on a day off school – not much.

Too young to go for a pint, too old to hang around with their parents, the friends have so far visited the shops, sat in the park and talked about the football. The only unusual thing about their day is that they have to be off the streets by 9pm – or risk arrest.

Last night a curfew came into force in the centre of Bangor that bans under- 16s from being in the area without an adult.

It is the first order of its kind to cover an entire city centre in the UK and has already been condemned by human rights groups who have labelled it more North Korea than North Wales.

Ned, 13, and his friends don't look much like a threat to the social fabric of Bangor. "It's just stereotyping," he says. "There are bad areas and a few bad young people, but we're not all like that." His friend Sam, also 13, is somewhat more direct. "It's stupid," he said.

Best known for its large university and picturesque setting, Bangor, nestled between the mountains and the sea in the county of Gwynedd, is an unlikely setting for a battle over civil liberties.

But according to Gwynedd Council and North Wales police, the problem of antisocial behaviour in the city has become so severe that a draconian new dispersal order is necessary.

The order, which covers the cathedral grounds, the university and the main high street, came into effect yesterday and will last for six months.

As well as banning under-16s from the area between 9pm and 6am, it also gives police the power to order groups of two or more people of any age to leave the area. Failure to comply could carry a £2,500 fine or a three-month jail sentence.

The professed purpose of the curfew and dispersal order is to allow people to "enjoy their lives without being intimidated or harassed", but opinions differ among locals about quite how intimidating a place Bangor is.

"The last time I walked down the high street at night I was quite nervous," said Beryl Owen, 70, a pensioner who works in a charity shop in the city. "There were crowds of young people and you see that some of them have cans of drink in their hands. But this is a bit severe. I have a grandson of that age and I wouldn't like to thing that he'd be breaking the law by being out on the streets after 9pm. And they are out and about at that age these days."

Elaine Smith, 47, a shop manager with two sons aged over 16, was more supportive.

"Children shouldn't be out at that time of night – what would they be doing? I don't come down to the centre in the evening. I've not felt intimidated while living here but they do make a mess of the benches, writing their names on things."

The Local Government Association, which represents local authorities in all parts of the UK, says that this is the first such curfew it has heard of.

Inspector Simon Barrasford of North Wales Police said dispersal orders were "an effective weapon against antisocial behaviour". Police claim that Bangor has "persistent problems" of intimidation and harassment.

"Many people are working very hard to improve and regenerate the city centre as well as just wanting to enjoy their daily lives without being intimidated or harassed," he said. "Drinking in public has an adverse effect not only on visitors' perception but also on the quality of life of residents."

But not everyone agrees. David Jones MP, a Wales minister in the Coalition Government, is concerned that the law could be "discriminating against a large sector of the public".

Nick Pickles, director of the human rights watchdog Big Brother Watch, called the plan "madness".

"Criminalising every young person in Bangor – without any need for them to be engaged in any wrongdoing – is an unwarranted intrusion on to the civil liberties of thousands of perfectly law- abiding young people," he said.