2020 presidential candidates, Trump, Obama and others react to attack in New Zealand on Twitter

"We grieve with you and the Muslim community," former President Obama tweeted.

Sen. Cory Booker, a Democrat from New Jersey who plans to run for president in 2020, tweeted that he is "sickened" by the attack and is determined to work against hate.

Sen. Kamala Harris, a California Democrat who is also running for president in 2020 called the alleged gunman's actions as "evil and cowardly" and sends condolences with a heavy heart.

President Donald Trump wants the people of New Zealand to know that the United States stands with them and sends well wishes to those affected.

And Sen. Bernie Sanders, who also recently announced a 2020 presidential run tweeted "No one should have to fear for their life because of their religion."

Senate Majority Leader Mitch McConnell said America stands with the New Zealand Muslim community in mourning the deaths of those killed in the attack.