Dutch Queen Beatrix, who will turn 75 on Thursday, has announced she is abdicating in favour of her son, Prince Willem-Alexander, who will become king on 30 April.

Willem-Alexander, 45, is married to Princess Maxima Zorrigueta and has three young children.

Decades of grooming for the throne involved shaking off his image as a beer-drinking fraternity boy whose blunt comments upset the press and politicians.

Speaking in a television broadcast, Beatrix said she was stepping down because she felt Willem-Alexander was now ready to take her place on the throne.

"I am not stepping down because the tasks of the function are too great, but out of the conviction that the responsibilities of our country should be passed on to a new generation," she said.

"It is with the greatest confidence that on April 30 of this year I will pass on the kingship to my son, the Prince of Orange. He and Princess Maxima are entirely ready for their future tasks."

A constitutional monarchy, the Netherlands has reduced the involvement of the Royal House in politics.

The queen had taken part in forming government coalitions by appointing a mediator, a role that raised questions about undue influence on the democratic process and that was scrapped last year.

Sources close to the royal family said Beatrix did not want to go until she felt her son was ready and his children were old enough.

She also wanted to ensure that anti-immigrant, eurosceptic politician Geert Wilders, of whom she disapproved, was in no danger of assuming real political influence.

She alluded in speeches to the need for tolerance and multi-culturalism, comments that were seen as criticisms of Wilders' anti-Islamic views, while Mr Wilders criticised the queen when she donned a Muslim headcovering on a trip to the Middle East.

Mr Wilders' poor showing at the last election and loss of influence in politics, could well have contributed to her decision to abdicate.

With Willem-Alexander on the throne, the Netherlands is likely to revive the debate about the role of the monarchy and the high cost of maintaining the royal household, particularly when ordinary Dutch people are having to deal with austerity measures.

"There is an ongoing discussion about the role of the royals in a modern society, and that discussion needs to continue," said Diederik Samsom, leader of the Labour Party, which is part of Prime Minister Mark Rutte's coalition government.

As queen, Beatrix often headed trade missions, most recently in Singapore, and was involved in promoting Dutch defence sales in the Middle East.

Beatrix, whose full name is Beatrix Wilhelmina Armgard, Princess of Oranje-Nassau, Princess of Lippe-Biesterfeld, has been on the throne since 1980, when she took over from Queen Juliana.

Dutch queens have made a tradition of stepping aside for the next generation over the last century. Queen Wilhemina handed over to her daughter in 1948 after half a century on the throne.

Queen Juliana was in deteriorating mental health when she made way for the 42-year-old Beatrix in 1980.

Willem-Alexander, who has a degree in history and has specialised in water management, will become Willem IV and is the first Dutch king in more than a century.

Last year, the family faced tragedy when Willem-Alexander's younger brother, Prince Friso, had a skiing accident in Austria while going off-piste. He suffered a severe brain injury and is still in a coma.