Thousands of health workers take part in strike action in Northern Ireland.
Paramedics are among the workers participating in picket lines across the region on Thursday.
Workers from the Nipsa, Unison, Unite and GMB unions are organizing the action.
The 24-hour stoppage is the last full day of action by health sector unions, who are calling for safe staff, better wages and better mileage allowances.
There was an earlier strike action on December 12.
The Royal College of Nursing also took part in a strike over wages and safe staffing in December.
Anne Speed, from Unison, said that in the absence of talks, employees are “stepping out and stepping forward”.
“It is a terrible situation when trade unions that want to negotiate have all doors closed to them. It is therefore inevitable that this action takes place today,” she said.
“Health workers cannot stand idly by or remain silent. And why would they?”
Ms Speed also denounced Secretary of State Chris Heaton-Harris, who is currently traveling to the United States to encourage trade opportunities.
The Stormont assembly continues to move with no ministers in office.
Ms Speed said Mr Heaton-Harris has responsibilities in Northern Ireland.
“It is time for him to make tackling the crisis in our healthcare a priority. Recruiting and retaining staff and paying justice are just as important as trade,” she said.
“Our members also expect a concerted effort from all political parties to break this impasse.”
In a statement, the Northern Ireland Ambulance Service (NIAS) said it has been working with union representatives to identify services and roles that will be exempt from strike action to ensure a response continues to the most clinically urgent patients.
However, NIAS said it expects challenges throughout Thursday and plans to maintain the safety of those patients whose need is greatest.
It has urged the public to call an ambulance on Thursday only in life-threatening emergencies such as cardiac arrest, loss of consciousness, difficulty breathing, severe bleeding and others.
“Callers should not hesitate to dial 999 in the event of serious illness or injury, but other callers should consider other options, such as self-care, seeking GP or pharmacy advice or reporting to the emergency room,” the service said.
The spokesperson added: “NIAS respects the right of our employees who are union members to participate in industrial action.
“This action is being taken in relation to the national issues of pay and conditions and is a matter for the government and the unions.”