Image copyright EPA Image caption More than 6,000 police have been deployed around Hong Kong, a substantial segment of its police service

Scuffles have broken out between police and pro-democracy campaigners in Hong Kong during the visit of the most senior official from Beijing to go there since major protests in 2014.

Zhang Dejiang, the leader responsible for Hong Kong affairs, arrived amid discontent with alleged interference in the territory's affairs by Beijing.

Tight security is in place with more than 6,000 police officers deployed.

Protesters were forced back from the residence of the territory's leader.

A heavy police presence surrounds the building, where Mr Zhang was due to have dinner on Tuesday night.

AFP news agency reports that earlier, seven members of pro-democracy political party the League of Social Democrats were arrested after putting up protest banners. Three are still detained.

A leading pro-democracy activist was also wrestled to the ground by police outside Mr Zhang's hotel, the agency adds.

Mr Zhang said he was in Hong Kong "to listen to all sectors of society about what recommendations and requirements they have about implementing the principles of 'one country, two systems'".

In a five-minute speech on arrival, Mr Zhang 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".

Who is Zhang Dejiang and what is he doing on the trip?

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.

Image copyright AP Image caption Zhang Dejiang brought the "warm regards" of the president

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.

Why is the trip contentious?

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.

Image copyright AFP Image caption A protest in September 2014, following a key political ruling

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.

Who are the protesters and what are their concerns?

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.

Image copyright AP Image caption Rioters in Mong Kok in February lifted the lid on the so-called "localist" groups considered a more radical force in Hong Kong politics

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.

What are the security measures for the visit?

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.

Image copyright EPA Image caption A giant banner calling for universal suffrage was swiftly removed from Hong Kong's Beacon Hill

Image copyright EPA Image caption Workers in Hong Kong were seen gluing down paving stones earlier this month, with lawmakers speculating it was to secure them ahead of the visit

Image copyright EPA Image caption Huge barriers have cordoned off security zones in central Hong Kong

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.