Donald Trump has denounced as a "horrible massacre" the deadly terrorist attacks on Muslim mosques in New Zealand, amid reports that the perpetrator -- a white supremacist -- is an admirer of the US president.

In a tweet on Friday, Trump condemned the terrorist attacks and expressed his condolences to the people of New Zealand after shootings at two mosques in the city of Christchurch had earlier in the day left at least 49 people dead and several others injured.

"My warmest sympathy and best wishes goes out to the people of New Zealand after the horrible massacre in the Mosques. 49 innocent people have so senselessly died, with so many more seriously injured. The US stands by New Zealand for anything we can do. God bless all!" Trump tweeted.

In a separate statement, the White House lashed out at the shootings but stopped short of mentioning specifically that the assault took place at a mosque or that Muslims were killed.

"The United States strongly condemns the attack in Christchurch. Our thoughts and prayers are with the victims and their families," White House Press Secretary Sarah Huckabee Sanders said in the statement.

"We stand in solidarity with the people of New Zealand and their government against this vicious act of hate," she added.

The attacks were conducted on two mosques in New Zealand�s Christchurch during Friday prayers, claiming the lives of 49 worshipers and wounding more than 20 others.

Forty-one people were killed at the al Noor mosque on Deans Avenue, said Mike Bush, New Zealand�s Police Commissioner. Seven people died at the Linwood mosque on Linwood Avenue, and one person died from their injuries in the hospital.

49 killed in �terrorist� attack on mosques in New Zealand

At least one gunman has killed 49 people and wounded more than 20 during Friday prayers at two New Zealand mosques.

Security officials in New Zealand said four people had been detained following the shooting, including one Australian.

The Australian gunman, identified as Brenton Tarrant, had broadcast on Facebook live footage of the attack on one of the mosques and published a "manifesto" in which he denounced immigrants, calling them "invaders.”

In his manifesto, Tarrant praised Trump and said he saw the US president as “symbol of renewed white identity and common purpose.”

This image grab from a self-shot video that was streamed on Facebook Live on March 15, 2019 by the man who was involved in two mosque shootings in Christchurch shows the man in his car before he entered the Masjid al Noor mosque. (Photo via AFP)

New Zealand�s Prime Minister Jacinda Ardern condemned the incident as an act of terrorism, saying at a press conference on Friday that the suspects held "extremist views" and had no place in New Zealand or the world.

"It is clear that this can now only be described as a terrorist attack,” Ardern also said on Twitter. "What has happened in Christchurch is an extraordinary act of unprecedented violence. It has no place in New Zealand. Many of those affected will be members of our migrant communities — New Zealand is their home — they are us."