Protesters have formed a picket line outside an ambulance centre in support of strikes.
Ambulance staff across the country are striking in a dispute over pay and working conditions.
In Brighton, staff and supporters gathered outside the city's ambulance centre.
Staff wore their uniforms and held signs which read "Not Safe, Not Fair" and "Too tired to care".
The strike is led by the GMB union, a trade union which has more than 460,000 members in different sectors from retail to education and health.
Ambulance staff follow the lead of nurses, who went on strike across England and Wales last week.
In the South East Coast Ambulance Service region, the GMB Union balloted members for industrial action and met the legal threshold to take action.
GMB issued a formal notice for strike action for December 21 from 6am to 11.59pm and the same hours on December 28.
Ben Leeves, a paramedic and Brighton's GMB rep, said: "We are protesting against the Government cuts to our service that are stopping us from delivering the care we want to deliver.
"Our patients are suffering day in day out and people have had enough.
Mr Leeves added: "We regularly work 12 and 14 hour shifts.
"We end up going to patients who have been waiting for us many hours, who are then much poorlier when we called."
A spokesman for Secamb said: "Following the announcement of industrial action, we have worked closely with our unions and all staff to ensure that the impact of any industrial action on our patients is kept to a minimum.
"We have worked with our local GMB Union branch to agree an approach for the days when industrial actions is taking place.
"This has focused on consideration to support colleagues’ right to take action in collaboration with potential impacts on patient care. The priority throughout has been balancing patient safety with the right to strike."
There has been some confusion over which incidents are considered "life-threatening" and will therefore still be provided with ambulances.
The spokesman for Secamb added: "As ever, we will be working hard to respond to patients and prioritising our response to our most seriously ill and injured patients.
"Anyone not facing a life-threatening emergency is likely to wait longer for a response or be directed to alternative care."
The health secretary Steve Barclay said some decisions about what will be covered during strikes by ambulance workers will be taken on the day.
Mr Barclay accused trade unions of making a “conscious decision” to “inflict harm” on patients in England and Wales by striking.
Rachel Harrison, the GMB union national secretary, said Mr Barclay was “insulting” ambulance workers.
Mr Leeves said: "We are protesting peacefully outside Brighton's ambulance centre.
"We are not stopping people from coming to work or ambulances from leaving the centre.
"Staff will be responding to life threatening calls.
"We hope to resolve this issue and we stand in solidarity with striking nurses too."
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