Whanganui and Nagaizumi-cho became sister cities in 1988. Nagaizumi was chosen due to its demographic similarities to Whanganui and rural nature, as well as the likely prospect of mutual benefits. There are now strong social, cultural, sporting and educational links between the two cities.There have been a number of official visits, led by the Mayors of both cities. A Whanganui delegation attended the 10th anniversary celebrations of the sister city relationship in Nagaizumi-cho in 1998 and a group visited in 2008. School parties from both cities regularly participate in exchange visits.
In 1983 Whanganui formed a sister city relationship with Toowoomba.Sister city visits between Whanganui and Toowoomba have largely focussed on gardens and flower festivals. Official activities have included attendance at the Australian Festival of Flowers as well as participation in the Whanganui in Bloom Parade.