The Reserve Bank's disclosure it had intervened in the currency market in the past month sent the currency sharply lower for a brief period on Wednesday.
Westpac currency strategist Imre Speizer said the bank wanted to send a signal to the market that it doesn't want the currency to go much higher.
But Mr Speizer says the market wasn't aware of the intervention at the time.
"Those interventions, or their sale of kiwi dollars, would have been done in fairly moderate amounts and kept quiet, what we would call covert intervention."
Mr Speizer said 'overt' intervention is usually done in much larger amounts, spans a longer period and has a more obvious effect on the kiwi over a few months.
He said covert intervention usually has a signalling effect when the transactions are published on the Reserve Bank's website, usually about a month after the end of the month in question.
Mr Speizer said there's no update yet for the month of April, but when it comes it should reflect some sale of the kiwi.