Sydney - Unemployment in Australia rose to 5.7 per cent in March from 5.2 per cent in January, official figures released Thursday showed.

It was the biggest monthly rise in joblessness in 18 years and took most analysts by surprise.

The Australia Institute, a private think tank, estimated the real rate of unemployment at 11.7 per cent because of the way the labour force is measured. Anyone who works for an hour a week is considered employed.

"For every person officially recorded as unemployed there are some 1.2 people, the hidden unemployed, who would also like to work and are available to start," the institute's David Richardson said.

Employment Minister Julia Gillard said the government had spent billions of dollars to stoke demand in the economy and protect jobs.

"We were told by some to wait and see, to sit back and just let worse figures than these roll in the door before doing anything," she told reporters in Canberra. "Well, we deliberately and decisively rejected that approach. We acted in anticipation of these figures." dpa