When a group of US high school students penned a letter to the Chinese President earlier this year they didn't expect a response, so they were "very surprised" when a top Chinese diplomat personally delivered a reply from Xi Jinping himself.

Key points: The Chinese President said the younger generation is the future of Sino-US friendship

The Chinese President said the younger generation is the future of Sino-US friendship Chinese social media users praised Mr Xi for personally writing the letter

Chinese social media users praised Mr Xi for personally writing the letter Mr Xi also reportedly wrote a letter to Italian students, urging them to be the "Marco Polos" of the new era

The first-year Mandarin Chinese students at Niles North High School in Illinois reportedly wrote to Mr Xi around Chinese New Year, sending their holiday wishes but also asking him about his work, life, hobbies, and opinion of America.

Mr Xi replied by saying that his job is "very tiring" but makes him very happy and that he is "deeply impressed" by the country's "beautiful sceneries, warm people and diverse cultures".

"I have also made many American friends, including young American friends," he wrote in a goodwill letter published by Chinese state-owned media Xinhua news agency.

"My job is to serve the people, very tiring, but it makes me very happy.

"I have a strong interest in philosophy, history, literature, culture, music and sports, and many of my hobbies developed from middle school and have been maintained ever since."

Mr Xi's own high school experience was cut short by the Cultural Revolution in 1966-1976, when the then 16-year-old was sent to rural areas along with millions of other youths to be re-educated by farmers and labourers during the tumultuous communist period.

Mr Xi's letter was reportedly met with enthusiasm by the Illinois students.

According to local media outlet Chicago Tribune, every high school student in the class was asked to write a letter as part of a class project.

The students reportedly voted on which of their letters would be sent, and eventually decided on the one written by freshman Kendra Le.

"I was surprised, very surprised," Mr Le told Chicago Tribune.

"It was an honour to receive a letter from him."

'Why did I get tears of joy in my eyes after reading the letter?'

Xi Jinping said the younger generation are the future of Sino-US friendship. ( AP: Andrew Harnik )

Mr Xi's letter, which was personally delivered by Zhao Jian, the consul-general of the People's Republic of China in Chicago, also encouraged the students "to contribute to the friendship between the Chinese and American people".

"I hope you will continue to 'add oil' [work hard] and make greater progress in your Chinese study," he wrote.

"The younger generation are the future of Sino-US friendship."

The Chinese President ended the letter by inviting the students to visit China, noting that it is better to see something once than to hear about it a hundred times.

While social media users on Twitter were sceptical whether the President's letter was genuine — with one person saying it was hard to "promote friendship" when most forms of communications are "outlawed" — it received an overwhelming positive response on Weibo.

"Why did I get tears of joy in my eyes after reading the letter?" one Weibo user commented.

Another user on the Chinese social media platform dubbed Mr Xi as "everyone's parent" in China.

While the class from Niles North High School were surprised about the response, it was not the first time the Chinese President has written to foreign students.

According to Chinese media reports, Mr Xi last month also responded to a letter penned by Italian students which encouraged them to be the "Marco Polos" of the new era by promoting Chinese-Italian cultural exchanges.

Despite this, Mr Zhao, the consul-general, told Chicago Tribune Mr Xi's response was unusual because the President received many letters from workers and farmers in China.

"The President is very busy," Mr Zhao said.

"It is my impression this is the first time he has written back to American students.

"They expressed a deep interest in the Chinese language. They showed strong feelings."