The Danish prime minister has called an election for June 18 in which her centre-left Social Democrats will face stiff competition from the centre-right Liberals who want more curbs on immigration and limits on state spending.

The polls suggest the Liberals and their allies will win, which could result in a coalition that includes the eurosceptic Danish People's Party, winner of EU parliamentary elections last year.

A centre-left bloc comprising Helle Thorning-Schmidt's Social Democrats and their supporting parties is about 7-8 percentage points behind a centre-left grouping led by the Liberals, according to the polls.

The Social Democrats have spent most of their time in power trailing behind the Liberals in the polls, sometimes with a gap of over 16 per cent.

But since April, the party has topped opinion polls for the first time since 2011. The government sharpened its tone on immigration and launched a slew of measures including a £3.7 billion spending plan.

"The plan is the roadmap that Denmark needs," Ms Thorning-Schmidt told journalists at a news conference held in her office.

"Therefore now is the right time to ask Danes whether we should stick to that direction or choose the experiment from the opposition."

The government's new measures have helped Ms Thorning-Schmidt's popularity, which was also boosted by her handling of the February attack by a radicalised Muslim youth in Copenhagen and because Liberal leader Lars Lokke Rasmussen has lost some credibility over past financial scandals.

Commentators say these factors will give Ms Thorning-Schmidt her best chance of defeating the Liberals.