Northern Ireland's entire public transport system has been halted while hospitals and schools also face disruption as public sector unions stage a mass strike.
More than 200,000 workers across the province will take industrial action in protest at public sector pension cuts, with representatives also objecting to wider Government spending reductions.
The Northern Ireland Public Service Alliance, representing members across the civil service, will alone have more than 45,000 workers on strike and stage 160 pickets.
All of Northern Ireland's 1,200 schools face disruption to transport and catering services, and with most of the teaching unions striking, it is likely that a majority will be forced to close their doors. In the health sector, emergency services are to be maintained and GP services and ambulances will be kept running despite disruption caused by industrial action.
The private sector has been critical of the day of action, but assistant general secretary of the Irish Congress of Trade Unions Peter Bunting defended the strikes.
"I think today is necessary because the public sector workers, and workers in general, are facing in many cases very, very serious reductions in their terms and conditions of employment," he said. "And it will impact on the quality of life of everyone."
Mr Bunting said cuts were removing money from the economy and would impact on both the public sector and the private sector. He added the significance of the strike action went further than protecting public sector pensions as union members were also mobilising against wider Government cuts which he said had failed to bolster the troubled economy.
"It is also putting down a marker that we will oppose the austerity cuts that have not worked and will not work," he said. "We need a Plan B."
He cited economic projections which he said showed Government policies had failed to promote real economic growth. Mr Bunting said the Government should look elsewhere for revenue and said £123 billion was lost in tax evasion, tax avoidance and through unclaimed tax.
"It is just incredible what is happening here," he said, arguing that a policy of cuts was "threatening the future of our children".