Some will not be done until the very end of the year, weeks after they were predicting about 20 emergency Covid-19 patients a day.

All were still building negative pressure rooms, the gold standard for preventing the airborne virus from spreading through corridors or air conditioning.

Some doctors and nurses were frustrated, saying the work should have been done months ago.

They worried where they would put Covid-19 patients if the ED was busy, with corridors even less suitable than before as a backup.

Middlemore Hospital's emergency department still has five more negative pressure rooms to build, with work likely to be finished next month. It currently has three.

Auckland Hospital is building nine more and they are not due to be finished until December. It currently has six between its adult ED and an assessment unit.

North Shore Hospital has four negative pressure rooms in its ED and assessment unit. It is planning to build four more but the work is not due to be finished until the end of December.

Longer-term, it will build another nine.

There is just one negative pressure room in the smaller Waitakere Hospital, with work underway to build two more by next month.

The figures were provided by the city's three district health boards.

All said they were well prepared to deal with an increase in Covid-19 patients safely - and there were measures other than negative pressure rooms that helped.

They included closed-door rooms, and well-ventilated spaces and separate triage streams for suspected Covid-19 patients.

They said most Covid patients would not need to be treated in negative pressure rooms.

College of Emergency Medicine president John Bonning said when Covid took off in the community it would be a tough run, especially for staff.

They would need to "strap in" but the health system would cope, he said.