Zhang Dejiang, the leader responsible for Hong Kong affairs, arrived amid discontent with alleged interference by Beijing.
Mr Zhang said he was in Hong Kong "to listen to all sectors of society".
More than 6,000 police have been deployed amid planned protests by pro-democracy groups.
In a five-minute speech on arrival, Mr Zhang, 69, conveyed "President Xi Jinping's warm regards and well wishes for the people of Hong Kong" and said he came "with the care of the central government and all Chinese people".
Noting his trip had "attracted wide attention", he said:  "I will listen to the chief executive and the [Special Administrative Region] government regarding their work, and to all sectors of society about what recommendations and requirements they have about implementing the principles of "one country, two systems".
He heads China's Hong Kong and Macau affairs office but is also chairman of the National People's Congress Standing Committee, making him China's third-highest ranking leader after President Xi and Premier Li Keqiang.
Mr Zhang is to speak at a policy conference on President Xi's One Belt, One Road economic project that aims to improve connectivity between China and Eurasia.
He will meet a group of four pro-democracy legislators at a reception, ahead of a banquet.
As head of Hong Kong affairs, Mr Zhang was responsible for a key decision in 2014 on Hong Kong's political future and is the highest-ranking mainland official to visit since then.
The mini-constitution, or Basic Law, under which Hong Kong is governed, says the ultimate aim is for the leader to be elected by universal suffrage.
Although China had promised direct elections by 2017, it said in 2014 that the leader, or chief executive, put up for election would come from a list of two or three candidates chosen by an effectively pro-Beijing nominating committee, angering pro-democracy campaigners.
The decision led to full-scale protests, dubbed the Umbrella Movement. Tens of thousands of protesters camped in the streets for weeks but the camps were gradually dismantled with no concessions from the government.
Current Chief Executive CY Leung remains unpopular. Commentators will be watching and listening carefully to see whether Mr Zhang will hint at endorsing him for another term.
Following the 2014 protests, a number of so-called "localist" groups sprung up and showed themselves willing to use violence to battle what they see as a dilution of the city's identity, fearing growing social and political influence from mainland China.
In February, hundreds of demonstrators dug up and threw bricks during a violent clash with police trying to shut a night food market. The market was seen by the protesters as a symbol of local traditions.
There have also been increasing concerns over the freedoms Hong Kong enjoys - unseen on the mainland - which were integral to the agreement that enabled Hong Kong to be returned to China by the British in 1997.
They include freedom of speech, the press, assembly, association, travel and trade union membership.
One incident that raised particular concern was the disappearance of five Hong Kong booksellers known for publishing controversial books about Chinese leaders.
The men were later found to have been detained by mainland authorities in a move condemned by the UK.
In addition to the 6,000 police officers on duty, hundreds of huge, water-filled plastic barriers have been deployed near Mr Zhang's hotel and the convention centre at which he will speak.
Demonstrators will be given designated areas and are unlikely to be visible to Mr Zhang.
Pavement stones have reportedly been glued together to prevent them from being ripped up and thrown by protesters.
The South China Morning Post said security was tight at the airport for Mr Zhang's arrival. It said guards reportedly took away journalists' umbrellas, along with a small yellow towel used by one reporter to cover a camera lens.
The colour yellow, along with umbrellas, has become a symbol of the pro-democracy movement.
Hours before Mr Zhang landed, activists unfurled a yellow banner on Hong Kong's Beacon Hill reading:  "I want genuine universal suffrage". The banner was later removed.
On Monday a Hong Kong man was arrested just over the border in Shenzhen for trying to buy a drone purportedly to be used to disrupt the visit.
Tight security is in place in Hong Kong for the visit of the most senior official from Beijing since large pro-democracy protests in 2014.