Beijing's top adviser on the Basic Law says the One Country, Two Systems principle will have to be improved, but Hong Kong's constitutional order won't change before 2047.

Shen Chunyao made the comments in a keynote speech at a legal conference on Friday ahead of the 25th anniversary of the handover.

He said people's focus should be on the correct implementation of One Country, Two Systems, and on accurately mastering the relationship between the nation's constitution and the Basic Law to protect everyone’s interests, as well as the SAR’s prosperity.

Shen said: "Fifty years is only a symbolic expression. This would not change even after 50 years. The first 50 years is: we cannot change, then after 50 years that would be that we need not change, as long as we believe in One country, Two systems. Its life, its vitality would be fully expressed."

He also said that One Country, Two Systems will need to be improved or fine-tuned as time changes, to ensure the SAR moves steadily ahead.

"We should not adopt a straitjacket approach. We shouldn’t think that once it’s set nothing can be changed, because if we just simplistically say that we will insist on this without being able to improve it with time, then we will not be able to fully develop its potential."

Earlier, Chief Executive Carrie Lam opened the conference by reiterating that Hong Kong will prosper as long as it acts in accordance with the Basic Law.

She said the SAR has faced its most significant challenges since the handover, adding that the turmoil of the extradition bill protests made her realise that any deviation from the original intention of One Country, Two Systems would lead to disastrous consequences.

Lam said: "Facing such a huge challenge as the chief executive of the SAR, I felt evermore clear that without a country there is no home, and I firmly believe that if we base our actions on the constitution and the Basic Law, and rely on the strength of the motherland, then Hong Kong will be stable and prosperous."