Stroke by stroke, the white paint goes on thick against the black cloth spread on a Hong Kong rooftop.

The Chinese characters are bold, and so are the accusations against the Beijing government.

"You have lied and cheated us out of democracy." "Enough with the empty promises." "Stop brainwashing students with your so-called patriotic curriculum."

You couldn't get away with banners like these in the rest of China, but Hong Kong has been different. And activists across the city are determined to exercise their more liberal right to free speech as Chinese President Xi Jinping comes to visit.

Troops prepare Thursday for the arrival of Chinese President Xi Jinping at the People's Liberation Army (PLA) Hong Kong Garrison in one of events marking the 20th anniversary of the city's handover from British to Chinese rule. (Damir Sagolj/Reuters)

He's in Hong Kong to mark the 20th anniversary since the former British colony reverted to Chinese rule. At the time, Beijing promised to implement a principle known as "One Country, Two Systems" which would let Hong Kong keep its more democratic approach for at least 50 years — allowing some direct votes, an independent judiciary and a free media.

A couple of dozen activists gathered on the warehouse roof this week to get ready for the celebrations and the opportunity to protest.

Hong Kong rooftop sign painter Edith Leung prepares for demonstrations in favour of democracy. 'If we do not try to take one step, then the next step won't happen,' she told CBC's Saša Petricic. (Saša Petricic/CBC)

This, even as 11,000 Hong Kong police have been deployed, not only to keep President Xi from harm but also to keep him from being offended. A special order has banned all "insulting" political banners and slogans from the route of the official visit.

On this day, the rooftop itself is under police surveillance, though officers do not interfere.

"China is trying to carry out colonial rule on Hong Kong," said Edith Leung. She knows this week's protest likely won't change anything. The banners may not even be seen by Xi. But students and even many older activists have been taking every opportunity to push for democratic self-government.

The rooftop being used in Hong Kong for preparing protest signs was under police surveillance, though they didn't interfere. (Saša Petricic/CBC)

"If we do not try to take one step, then the next step won't happen," said Leung. Next to her, Au Nok Hin added: "What we try to persuade the Chinese government is simply, we want you to keep your promise."

Big protests are planned for July 1 in central Hong Kong. Several smaller ones have already taken place, including the occupation of a monument meant to symbolize Chinese friendship. Twenty-six protestors were arrested and held for more than a day.

Among these were Joshua Wong and Nathan Law, two protest leaders instrumental in bringing more than 100,000 out into the streets for months as part of the Umbrella Movement in 2014. The sit-in was a demonstration against Beijing's decision not to allow universal voting for the Hong Kong government.

Students and even many older activists have been taking every opportunity to push for democratic self-government. (Saša Petricic/CBC)

After largely leaving Hong Kong to run its own affairs in the early years after taking over, recently Chinese leaders have stepped in more and more aggressively.

In one bizarre incident, Chinese security agents are accused of kidnapping Hong Kong booksellers for distributing politically sensitive works and whisking them across the border into mainland China in 2015. The men later offered televised confessions to other crimes, though at least one insisted he was coerced.

Chinese President Xi Jinping inspects troops at the People's Liberation Army (PLA) Hong Kong Garrison in one of events marking the 20th anniversary of the city's handover from British to Chinese rule, in Hong Kong Friday. (Damir Sagolj/Reuters)

Last year, Beijing intervened in court decisions which banned two pro-democracy members of Hong Kong's legislature from taking their seats after being elected.

That territory-wide election saw record support for the movement, including more votes for more radical protest activists than ever before.

For political activist-turned political scientist Brian Fong, that means Beijing risks having the situation spiral out of control every time it intervenes. He teaches at the Education University of Hong Kong.

Henry Ho: real reason for assertiveness. (Saša Petricic/CBC)

"We have been trapped in a vicious cycle," Fong says. "Beijing tries to stabilize the Hong Kong situation by intervening more. But once it intervenes, people start to resist more and then Beijing gets more worried. And so on."

The debate has been getting more extreme, with some now saying the only way Hong Kong can achieve true democracy is by separating from China.

It's not a widespread view here, but just raising it is enough to guarantee a tough response from Beijing. People in other parts of China have been accused of terrorism for advocating independence for their regions.

Beijing supporters in Hong Kong like Henry Ho say that's the real reason for China's recent assertiveness. He belongs to a think-tank that advises Beijing leaders, the One Country, Two Systems Youth Forum.

He says hardliners in Beijing may not like criticism of China or the Communist Party, but they will grudgingly allow that in Hong Kong. "But if you go beyond that red line to pursue the path of independence," Ho says, "then it won't be tolerated."

Chinese President Xi Jinping, right, is greeted by tycoon Li Ka-shing before a photo session during Xi's visit in Hong Kong on Friday. Xi landed in Hong Kong Thursday to mark the 20th anniversary of Beijing taking control of the former British colony. (Bobby Yip/Associated Press)

Anson Chan says Beijing has been heavy handed with more minor issues, and way too frequently. She is a former Chief Secretary of Hong Kong, the top civil servant at the time the British colony passed to Chinese control.

"It's little wonder that Hong Kong people increasingly identify themselves as 'Hongkonger' rather than Chinese," she says. "Particularly our younger generation."

And she warns that the protests could grow and "nobody can predict how far things will go" if Chinese leaders don't lay off.