More and more hospitals are feeling the pressure of winter illnesses, with patients being told to stay away unless they are seriously sick.

Both North Shore Hospital and Waitakere Hospital in Auckland were experiencing high demand and occupancy levels, Waitemata District Health Board said on Thursday.

The DHB's acting chief medical officer Dr Jonathan Christiansen asked people to "think twice" before going to the emergency department at either hospital.

"Emergency departments are for seriously unwell patients in need of emergency care, and patients with less serious health concerns could delay treatment for patients in serious emergency situations," he said.

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On Saturday, Auckland District Health Board made the same plea as it revealed Auckland City Hospital had experienced its busiest four-week period ever up to July 9.

In June, Middlemore Hospital in south Auckland reached 105 per cent capacity, with more than 350 patients coming into the hospital each day.

Hospitals in Taranaki, Wellington, Waikato and Southland were also overwhelmed, with staff working extra shifts and patients facing long waits for beds.

Christiansen said all patients needing immediate hospital-based attention would still receive the treatment they required.

A number of conditions could be treated in non-emergency settings, reserving the ED for emergency use only, he said.

The DHB was urging people with less serious health concerns to call Healthline on 0800 611 116 or visit their GP.

Alternatively, they could also get advice and treatment for common minor illnesses from community pharmacists, or attend an accident and emergency clinic after hours, Christiansen said.