WELLINGTON -- New Zealand's central bank will this week introduce the Chinese renminbi into its trade-weighted index (TWI) to reflect changes in the country's trading partners.

The new TWI, a measure of the value of the New Zealand dollar relative to the currencies of the country's major trading partners, would include 17 currencies, replacing the current five-currency TWI from Wednesday, said a statement from the Reserve Bank of New Zealand (RBNZ) on Monday.

The weights for each currency will be based on the two-way trade in goods and services between the foreign country and New Zealand.

Data on trade in services, representing about 25 percent of New Zealand's total trade, is to be included in the calculation of the weights for the first time.

Since it was introduced in the 1970s, the TWI had been a weighted average of five exchange rates -- the greenback, euro, yen, Australian dollar and pound that formerly accounted for the bulk of New Zealand's trade, RBNZ assistant governor and head of economics John McDermott said in a statement.

As trade had grown, particularly with China, these five countries now accounted for less than half of New Zealand's trade.

The new approach would include the exchange rates of countries and regions that now accounted for more than 80 percent of New Zealand's foreign trade.

The weights for the 17 currencies, the Australia dollar is given the biggest weighting, followed by the Chinese renminbi, the US dollar, the euro, and the yen.