"Hate speech is spreading like wildfire in social media. We must extinguish it," he said during a visit on Tuesday to the al-Noor Mosque which was targeted in a deadly attack by a suspected white supremacist on March 15.

"Social media is being exploited as a platform for bigotry and we must all show solidarity in response to this dangerous upsurge in hatred," he added.

Guterres said he had picked Christchurch as destination for his annually solidarity visit "because of the terrible terrorist attack against your community," the secretary-general said.

"I wanted to come here personally to transmit love, support and total and complete admiration," he added.

While Guterres said he had ordered a United Nations team to develop a "global plan of action" to deal with hate speech online, New Zealand's Prime Minister Jacinda Ardern has travelled to Paris to host the so-called Christchurch Call alongside French President Emmanuel Macron.

The summit will be held on Wednesday and will see tech company and country leaders commit to an agreement that aims to prevent social media being used to promote and organise terrorism in the wake of the Christchurch attack, in which 51 people died.

Australian Associated Press