New 3 and 4 wheeled delivery vehicles were unveiled by NZ Post in New Plymouth today that will deliver both letters and parcels to residential addresses.

New Plymouth residents will be the first in the country to experience the latest in postal delivery technology.

New Zealand Post will next week introduce high-tech three and four-wheeled vehicles to deliver mail and parcels in the city.

The vehicles can handle as much mail as four posties and will be trialled in New Plymouth before being rolled out around the rest of the country next year.

NZ Post chief operating officer for delivery, Ashley Smout, said a decline in residential mail and an increase in parcels were behind the beginning of the vehicle service and New Plymouth was chosen as the test ground because of its geography.

"New Plymouth represents the cross section of both businesses and residential areas," he said.

"The terrain is both flat and hilly and so it gives us a chance to see how the vehicles perform in a range of environments."

Smout said the vehicles were designed for the conditions and already used in Europe.

"We have made some pretty minor adjustments for things like the weather here, the wind and the rain, to give our people that extra protection but they're largely the same vehicles used in Europe."

Smout said online shopping was fuelling an increase in parcels.

"The exciting thing for us is that the vehicles give us a whole new opportunity to improve our parcel delivery services and give New Zealanders a new look NZ Post," he said.

"On the first of July we have the frequency change, which will see standard mail in residential areas being delivered three days a week instead of six.

"But for priority mail and priority parcels, they will still be delivered six days a week."

Smout said the company was working on giving customers more choice on when and how parcels were delivered and enabling them to do such things as sign over authority for the parcel.

"This means we can leave the parcel around the back, or we might be able to leave it with a neighbour, or drop it into a supermarket or gas station and customers can pick it up from there."

People can go to www.nzpost.co.nz to see how the delivery changes affect them.