Members from Unison, Nipsa and GMB are involved.
Health workers have been told they will receive a 2022-23 pay award of £1,400, however, Unison’s regional secretary said “it’s not enough”.
The union said the uplift would not settle the dispute as it was lower than inflation.
Monday’s strike in the health service is the first since 2019.
The chief executives of the local health trusts said contingency plans were in place to protect critical services and that they “obviously want to see all staff properly rewarded for their work”.
Social worker James Kehoe was among those striking at Altnagelvin hospital in Londonderry.
Mr Kehoe said health workers did a “sterling job” during the Covid-19 pandemic “when we got the claps from the politicians”.
“Claps don’t fill your oil tank, don’t pay your electricity bill,” he added.
Speaking from Antrim Area Hospital, staff nurse Yvonne Hegarty said it felt “degrading” to work in such a demanding job for what she described as “so little pay”.
Ms Hegarty said caring for patients was her priority, but it was hard while worrying about things like the cost of food and fuel.
Paramedic Gabriel McComish was on the picket line at the Royal Victoria Hospital in Belfast.
Speaking as cars drove by beeping their horns, Mr McComish said he believed those on strike had the support of the public because they were “fighting for better patient care”.
Domiciliary care worker Pamela McKenzie said she joined the picket line at Ards Community Hospital because she “can’t afford to live any more”.
Ms McKenzie said striking was “a very hard decision to make, but I have a family too. I have bills to pay”.
Nipsa deputy secretary general, Padraig Mulholland said people were “fighting back”.
Speaking to BBC Radio Foyle he said: “We are not prepared to see unsafe staffing become the norm in the health service.”
In a joint statement the chief executives of Northern Ireland’s health trusts said contingency plans were in place to mitigate disruption to services during the strike.
“We obviously want to see all staff properly rewarded for their work. They have been impacted heavily by cost of living increases and escalating pressures on health and social care services.”
The statement reiterated previous comments that the funding model for the health service made it “impossible to plan for the long term” and said the current system was “unsustainable”.
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