AFP - Thousands of workers protested in four Dutch cities on Saturday against a government decision to increase the state retirement age from 65 to 67 by 2025.

"We think it is wrong for the government to seek to achieve savings by making people work longer," Paulus Plas, a spokesman for the country's largest labour organisation, the FNV, told AFP.

Plas said 20,000 to 30,000 workers took part in each of the protests, the largest of which took place in the western port city of Rotterdam, where he said up to 20,000 showed up.

Police put participation in Rotterdam at closer to 5,000 and said the protest went off without incident.

The Dutch cabinet last month announced that the pensionable age would rise to 66 in 2020 and 67 five years later, citing deteriorating state finances and the need to boost labour participation as the Netherlands deals with a greying workforce.

"Currently, we have four working people for every pensioner; soon this will be two to one. What does this mean for the younger generations?" Dutch Prime Minister Jan Peter Balkenende said.

People would still be able to retire at 65 but on a lower pension, and there would be special protective measures for people who do many years of "heavy work."

Opposition political parties and labour organisations oppose the changes.

A recent FNV-commissioned opinion poll found that three quarters of Dutch nationals do not support the plan, believing that they would themselves be disadvantaged by it.

According to Plas, "people with the lowest levels of education, who start working earlier, earn less and have a shorter life expectancy will suffer the most."