Plank said hospital numbers were doubling roughly every five days and if that continued, the number of people in hospital on March 6 would be close to 800.
However, the shape of the outbreak was very difficult to predict, particularly because the current high case numbers were partly due to delayed PCR results, along with new rapid antigen test results, Plank said.
"It could be that those numbers are starting to slow, and hopefully that is the case," he said.
"The models at the moment are suggesting that we could peak at around about 1000 people in hospital in about three weeks' time but it does depend on what happens with cases."
Another scenario was the move to phase 3 - which had less contact tracing and fewer people isolating - could cause case numbers to rise.
It was possible, although less likely, hospitalisations would hit 2000 on any given day, he said.
- RNZ