Presidential candidates Hillary Clinton and Donald Trump reacted Sunday to a mass shooting at a gay nightclub in Orlando.

At least 50 people are dead and another 53 wounded from an attack on the Pulse nightclub.

(Related: 50 killed in Orlando gay nightclub; worst mass shooting in U.S. history.)

“Woke up to hear the devastating news from FL,” Clinton tweeted to her more than 6.8 million followers. “As we wait for more information, my thoughts are with those affected by this horrible act. -H.”

Police are investigating the shooting as a possible act of terrorism.

“Really bad shooting in Orlando,” Trump messaged to his nearly 9 million followers. “Police investigating possible terrorism. Many people dead and wounded.”

Four hours later, Trump added: “Horrific incident in FL. Praying for all the victims & their families. When will this stop? When will we get tough, smart & vigilant?”