Trump took to Twitter after his conversation with Ardern.
Trump first tweeted last night.
Ardern has also spoken to Australian Prime Minister Scott Morrison.
The Ministry of Foreign Affairs and Trade is receiving messages to New Zealand from around the world.
Ardern said she had received some from other leaders she personally knew.
They included Australian Labor leader Bill Shorten, Spanish Prime Minister Pedro Sanchez, and British Prime Minister Theresa May, European Union High Representative Fredrica Mogherini and European Commission Vice-President Frans Timmermann.
Pakistan Prime Minister Imran Khan tweeted his sympathy last night and in another tweet laid the blame at the post 9-11 environment in which "Islam and 1.3 billion Muslims have collectively been blamed for any act of terror by a Muslim."