Although police have started identifying some of those killed, many people are still waiting anxiously for news of their loved ones.

"We know it is a very difficult time for families waiting for information," Orlando Mayor Buddy Dyer said on Facebook. 

"As difficult as it is, we ask for patience, compassion and love. Pulse remains an active crime scene. Law enforcement is working the scene as efficiently and diligently as possible while being respectful to the remains of the deceased.

"We are setting up additional means of communication. We have the hotline, 407 246 4357, where it is important if you have a loved one that you believe is a victim to call."

Orlando's police have released the names of another two victims in addition to the four that were identified earlier.

Police say the number of dead in the Orlando shooting remains at 50, and urge to avoid "erroneous reporting".

People around the world have been expressing condolences to the relatives of the shooting victims, with hashtag #loveislove currently trending on Twitter.

In a tweet, Donald Trump reiterates his previous call for a ban on Muslim immigration.

The former wife of Omar Mateen said he was violent and mentally unstable and beat her repeatedly while they were married, the Washington Post reports., external

“He was not a stable person,” said the ex-wife, who spoke on the condition of anonymity because she feared for her safety.

She said they married in 2009 but divorced after only a few months. She says he was not particularly religious at the time.

Hillary Clinton's campaign says that a planned even on Wednesday with President Obama will now be postponed.

In an emailed statement, Mr Trump criticised Mr Obama and Mrs Clinton for not saying the words "radical Islam" in their respective statements. 

He even called for Mr Obama to step down and Mrs Clinton to leave the presidential race over it.

The presumptive Republican nominee also alleged that hundreds "of migrants and their children" were "implicated in terrorism" since 9/11.

"If we do not get tough and smart real fast, we are not going to have a country anymore. Because our leaders are weak, I said this was going to happen – and it is only going to get worse."

Trump says he will add comments on the Orlando shooting to his previously scheduled speech on Monday

AP reports that Los Angeles police are searching a vehicle in a busy thoroughfare in a mostly residential area of Santa Monica, California.

There were red plastic gas cans near the car. Los Angeles County Sheriff's officials said an armed man who was arrested earlier on Sunday told police that he was going to the pride parade to look for a friend. Authorities are now looking for that person.

Santa Monica Police spokesman Saul Rodriguez told the Los Angeles Times that detectives are "not aware of what the suspect's intentions were at this point.''

BBC's Rajini Vaidyanathan is reporting from Orlando and is now answering questions on our BBC News facebook page., external

Orlando's police have begun releasing names of some of the victims of the attack.

The police say that their relatives have already been contacted.

Bernie Sanders, a candidate for the Democratic nomination, said that "all Americans are horrified, disgusted and saddened by the horrific atrocity in Orlando".

"At this point we do not know whether this was an act of terrorism, a terrible hate crime against gay people or the act of a very sick person, but we extend our heartfelt condolences to the victims' families and loved ones and our thoughts are with the injured and the entire Orlando LGBTQ community."

Canadian Prime Minister Justin Trudeau has said in a statement he is "deeply shocked and saddened" over the Orlando shootings.

"We stand in solidarity with Orlando and the LGBTQ2 community," Mr Trudeau said. “We grieve with our friends in the United States and Florida, and offer any assistance we can provide.”

The Canadian prime minister is due to attend Toronto's Pride parade on 3 July.

Volunteers unload cases of water and sports drinks to be donated to victims' families.

Presumptive Democratic presidential nominee Hillary Clinton has said the shooting was "an act of terror".

She added: "To the LGBT community: please know that you have millions of allies across our country. I am one of them."