Hospitals across England are providing emergency care only after thousands of junior doctors went on strike.
Despite last-ditch talks to prevent the damaging action, around 4,000 operations and procedures have been cancelled, with thousands more routine appointments also postponed.
Around 100 picket lines have been put in place for the strike, with a large concentration in and around London.
Patients have been told hospitals are under pressure and asked to attend A&E only if they have a genuine emergency.
Instead, patients are being asked to make the most of other NHS services, including GPs, walk-in centres, the 111 phone line and pharmacies.