ANZ retail division's managing director Kerri Thompson says domestic and international conditions mean wholesale interest rate markets have been volatile.

"We're not sure how long this window will remain open. We hope to keep it open for a while but we'll be reviewing it on a daily basis," Thompson says.

It's ANZ's lowest one-year rate since at least 1995, she says.

While ANZ's rate is now the lowest "carded" one-year fixed rate, it doesn't beat Kiwibank's current one-year fixed special at 4.99% for those with at least 30% equity - Kiwibank's "carded" one-year rate is still 5.65%.

Kiwibank spokesman Bruce Thompson says the special "has been hugely successful. We're pushing towards $100 million of sign-ups." That's since it was introduced on April 26.

Those taking up the offer are a mix of existing Kiwibank customers switching and new customers coming from other banks, Thompson says.

The next lowest one-year rate in the market currently is HSBC's 5.29%, although that comes with special conditions, and then the Public Trust's 5.4%.

ANZ's move follows SBS Bank and sister bank HBS cutting their three and five-year fixed rates earlier this week, including even lower specials for customers with all their business with the banks and with at least 20% equity.

ANZ has also cut its six-month term deposit rate to 4% from 4.3% but kept its "serious saver" rate at 4.5%, its nine-month term deposit at 4.5% and its one-year term deposit at 4.6%.