The public is asked to only call an ambulance in an emergency on Thursday, as paramedics are set to strike in a row over pay.
Ambulance staff who are members of UNISON, Unite and GMB will take strike action for 12 hours from midday.
East Sussex NHS staff also plan to walk out from 9am, in a 12 hour strike.
In some parts of the country GPs have been asked to step in to help cope with demand while the strike takes place, but the South East Coast Ambulance Service (SECAmb) said this was not planned in this region.
A SECAmb spokesman said, “SECAmb has been working closely with its union representatives ahead of the planned industrial action on Thursday, which is on national rather than local issues.
“In previous industrial action on this issue the vast majority of our staff, while supporting the strike, continued to provide ‘life and limb’ cover for the most serious calls.
“We will continue to respond to life-threatening emergencies but other less serious calls may experience delays. With this in mind we are asking the public for their help by remembering that 999 should only be used in an emergency.
“While we expect the day to be challenging, we have robust contingency plans in place to ensure we can provide a safe and responsive service to those people who need us.
“These include increasing our ability to provide clinical advice in our Emergency Operations Centres, utilising our own response capable managers and increasing the support available from our volunteer community first responders.
“We will continue to be in close talks with union representatives to ensure that the impact on patients is kept to a minimum and thank the public for their ongoing support.”
Richard Sunley, chief operating officer at the East Sussex NHS Healthcare Trust, said, “We have been working with staff side representatives to try to anticipate the number of staff who will be taking industrial action between 9am and 9pm on Thursday, to ensure we have staff to provide essential services. Our overriding objective during this period of industrial action is to ensure we continue to provide high quality and safe services to patients.
“We do not anticipate any major disruption, however we do have contingency plans in place to ensure the quality of patient care is not compromised should there be any significant disruption to supporting services. Patients are advised to attend clinics and appointments as normal unless otherwise told.”
Following the strike, staff will work to rule from Friday and until February 24, followed a 24-hour strike on February 25.