Denmark on Thursday adopted legislation making daycare mandatory for all children over the age of one in disadvantaged neighbourhoods, and parents who do not comply will lose their family allowances.

"When some of these children start school, they risk being up to two years behind (their peers)," Social Affairs Minister Mai Mercado told news agency Ritzau.

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Disadvantaged neighbourhoods in Denmark tend to have large immigrant populations, with some children not learning Danish.

School is mandatory for all children from age six.

The reform - a deal reached by the centre-right government, the anti-immigration far right and the Social Democrats - will bring "only good things", Mercado said.

"We are offering a framework for learning, encouraging their language development and helping them prepare for school," she added.

A total of 43 neighbourhoods are concerned by the new legislation, which is to take effect on July 1, 2019, and has already come in for harsh criticism.

"It's obscene to discriminate against people living in Denmark based on where their residence is located and whether or not they live in a so-called ghetto," the head of Denmark's Council for Socially Marginalised People, Jann Sjursen, told Ritzau.

Earlier this year, Prime Minister Lars Lokke Rasmussen of the Liberal Party announced a "zero ghetto" target by 2030.

He said too many immigrants were living "concentrated in a small number of neighbourhoods", and behaving "differently" than "the average Dane".