South East Coast Ambulance Service has declared a "business continuity incident".
In a tweet, the service, which covers Kent, Surrey and Sussex, said: "Our staff are working hard but we remain extremely busy as do our local hospitals.
"As part of our escalation plans we’ve declared a Business Continuity Incident to help us manage the situation.
"Pls be patient if you need our help & consider alternatives to 999 where possible."
And on facebook earlier, the service posted: "It's another #ManicMonday for us & you can really help us by considering other options before calling 999."
Yesterday the service said it had more than 800 staff working hard, asking people to be kind to staff on the phone or face to face, be patient, and not to call back unless the patient's condition changes.
In March the service confirmed it had moved to its highest level of alert.