As the Yuletide season draws near, Republican presidential hopeful Donald Trump is encouraging Americans to focus on Jesus Christ, the true essence of Christmas.

The business tycoon, who earlier identified himself as a Christian and identified the Holy Bible as his favourite book, also called on Americans to use the greeting "Merry Christmas" more, not "Happy Holidays."

During an appearance at the Values Voter Summit on Friday, Trump lamented how many business establishments in the US no longer use the greeting "Merry Christmas."

"The word 'Christmas.' I love Christmas. I love Christmas. You go to stores, you don't see the word 'Christmas.' It says 'Happy Holidays' all over. I say, 'Where's Christmas?'," Trump said.

"I tell my wife, 'Don't go to those stores. I want to see Christmas. I want to see Christmas," he added.

The billionaire developer promised to correct this practice if he is elected to the White House.

Trump's call for the use of "Merry Christmas" instead of "Happy Holidays" is not new. In 2012, he posted this tweet: "7 of 10 Americans prefer 'Merry Christmas' over 'Happy Holidays' ... No surprise."

"I want to see 'Merry Christmas.' Remember the expression 'Merry Christmas'? You don't see it anymore. You're going to see it if I get elected, I can tell you right now," Trump said.

In the United States, "Happy Holidays" and "Season's Greetings" have gained popularity in department stores, public schools and greeting cards. These greetings are used from Thanksgiving Day, Nov. 26 this year, up to New Year's Day, Jan. 1.

"Happy Holidays" is a phrase that dates back to the 1890s but gained popularity in the 1970s, historians said.

The increasing use of "Happy Holidays" instead of "Merry Christmas" has become controversial in the United States, with advocates claiming that "Happy Holidays" is an inclusive greeting not meant to attack Christianity or other religions but as a response to the country's growing non-Christian population.

But critics of "Happy Holidays" say the greeting has a materialistic, consumerist, atheistic, politically correct and even an anti-Christian tone.

Trump booed for calling Rubio 'a clown'

In the same event, Trump once again attracted controversy on Friday when he called fellow Republican presidential hopeful, Florida Senator Marco Antonio Rubio, a "clown."

"You know there's this clown Marco Rubio, I've been so nice to him," Trump said.

Upon hearing this remark, the audience immediately booed Trump. The booing lasted for several seconds, despite Trump's attempt to pacify the crowd.

Trump and Rubio have been in a word war this past week, with the Florida senator describing Trump as "very thin-skinned" and "very sensitive to criticism."