U.S. President Donald Trump said Friday that he has agreed with Chinese counterpart Xi Jinping to join hands to tackle the new pneumonia-causing coronavirus.

"China has been through much & has developed a strong understanding of the Virus. We are working closely together. Much respect!" Trump tweeted following a phone conversation with Xi.

Xi expressed concern to Trump over the spread of the new virus in the United States, saying Beijing and Washington should maintain close communication to prevent further infections, according to Chinese state-run media.

The Chinese president, meanwhile, was quoted by the media as asking Trump to take "substantial" action to improve Sino-U.S. relations, which have remained in a fragile state amid a prolonged tit-for-tat tariff war and are now being further strained by the pandemic.

The number of people infected with the new coronavirus exceeded 500,000 on Thursday, a tally by Johns Hopkins University of the United States showed.

The new virus was first detected late last year in the central Chinese city of Wuhan, known as a business and transportation hub with a population of around 11 million.