Theresa May and Donald Trump have led world leaders in condemning the Christchurch terror attack.
A man in his 20s has been charged following the murder of 49 worshipper at two mosques in the New Zealand city.
- Read more: 49 killed in mass shooting at New Zealand mosques
- Read more: Christchurch shooter published 'manifesto' hours before attack
Mrs May tweeted: “On behalf of the UK, my deepest condolences to the people of New Zealand after the horrifying terrorist attack in Christchurch.
“My thoughts are with all of those affected by this sickening act of violence.”
US President Donald Trump described the atrocity as a "horrible massacre" and expressed sympathy for the people of New Zealand.
He added: "49 innocent people have so senselessly died, with so many more seriously injured.
"The U.S. stands by New Zealand for anything we can do. God bless all!"
'We stand in solidarity with the Muslim community'
Jeremy Corbyn at Finsbury Park Mosque.
Labour leader Jeremy Corbyn joined wellwishers in leaving floral tributes at Finsbury Park Mosque in London.
The Christchurch suspect had praised Darren Osborne, who attacked the mosque in 2017, in a manifesto published online.
Labour leader Jeremy Corbyn tweeted: “My heart goes to the victims of the horrific terror attack in New Zealand.
“We stand in solidarity with the Muslim community in Christchurch and around the world.
“We must defeat the bigotry which fuels such hatred and violence."
'Reassurance patrols' around UK mosques
Police officers stand guard outside Finsbury Park Mosque in London.
Home secretary Sajid Javid said he would be meeting with British police and security services to look at ways to protect British mosques.
He added: “We stand with New Zealand and Muslims acrss the world against all forms of racism and anti-muslim hatred.”
Mayor of London Sadiq Khan said the Metropolitan Police would also be stepping up “reassurance patrols” around mosques.
He added: “London stands with the people of Christchurch in the face of this horrific terror attack.
“London will always celebrate the diversity that some seek to destroy.”
'Disgusting' remarks by senator
An Australian senator has been criticised for drawing a link between the attack and immigration.
Queensland senator Fraser Anning tweeted: "Does anyone still dispute the link between Muslim immigration and violence?"
Australian Prime Minister Scott Morrison replied: "The remarks by Senator Fraser Anning blaming the murderous attacks by a violent, right-wing, extremist terrorist in New Zealand on immigration are disgusting.
"Those views have no place in Australia, let alone the Australian Parliament."