The number of constituent firms on Hong Kong's Hang Seng Index that have published reports on sustainability assurance grew to 65% in 2024 from 51% in 2023, according to a report by the city's Accounting and Financial Reporting Council released Monday.

The assurance could boost investor confidence, sustainability ratings, and brand reputation, the council said.

Of the 82 constituents on the HSI, 53% have a "limited" assurance rating, while 21% obtained a "reasonable" rating, and 19% obtained high or moderate assurance levels, the report said.

Thirty-eight percent of HSI constituent firms were given assurance ratings for their whole sustainability reports, the council said.

Reasonable assurance means auditors need to gather enough evidence to reduce misstatement risks to acceptably low levels, while limited assurance means auditors do not have clear evidence against claims by the reporting entity, according to a separate report by the South China Morning Post.