Jasmine Li was still a student when she opened her first offshore bank account through Mossack Fonseca Hong Kong, but the shady world she entered that day had been part of the city's underbelly for decades.

The granddaughter of China's then fourth-ranked politician was among dozens named in a vast cache of documents leaked from the Panama law firm that have given a glimpse into how the rich and powerful hide their money.

But the so-called Panama Papers, released by the International Consortium of Investigative Journalists this month, have also exposed the key role played by Hong Kong and Singapore in funnelling that wealth into tax havens.

Mossack Fonseca's Hong Kong offices were their busiest in the world, the ICIJ analysis showed, setting up thousands of shell companies including some linked to China's top political brass, the city's richest man, Li Ka-shing, and movie star Jackie Chan.

Experts say the Asian financial hubs have already channelled billions into tax havens, and the Boston Consulting Group predicts they will be the world's fastest-growing offshore centres over the next five years.

"Hong Kong is set up to make it easy for people to do business, and it is very easy to do business here," said Douglas Clark, a barrister with one of Hong Kong's largest chambers.

"But when it's easy to do business then it's easy to do any type of business, legal or illegal."

Offshore companies are not necessarily illegal, but they operate on the fringes of what is allowed and their opaque structures make it easy to conceal ill-gotten or politically inconvenient wealth.

They have proved a boon for Hong Kong and Singapore, which are known not only for their financial expertise but also light-touch regulation, discretion and non-cooperation with foreign tax authorities.

Both are already on regulators' radars -- the EU briefly added Hong Kong to its tax blacklist last year -- but experts say they are unlikely to do anything to jeopardise the lucrative offshore business.

- 'Turning a blind eye' -

Domiciling offshore has a long history in the region. In 1984, then trading house Jardine, Matheson & Co, one of the most powerful companies in Hong Kong's colonial history, relocated to Bermuda citing concerns about the city's handover to China.

"Hong Kong's history as a financial centre that specialises in turning a blind eye to things that would be investigated elsewhere goes right back to the 1960s," said financial commentator Tom Holland.

Today, Chinese investors use offshore companies legally in Hong Kong to bypass red tape, take advantage of tax breaks for foreign investors and circumvent strict capital controls.

Hong Kong University law professor Douglas Arner said it has become "perfectly normal" for companies to park money from overseas operations offshore, as the city does not tax profits made elsewhere.

But their widespread use has earned Hong Kong and Singapore reputations for murky dealings, and the Tax Justice Network ranked them among the least transparent places in the world in last year's financial secrecy index.

In Singapore, seen as more rigorous in policing its financial sector, the TJN said a culture has evolved of enforcing the law domestically but tolerating the illicit money that flows in from crimes committed overseas.

"Singapore is not only a secrecy jurisdiction... but also a tax haven, providing numerous tax avoidance and evasion opportunities," the group said in its profile of the city state.

- 'They'll find snakes' -

Clark said criminals, drug dealers, email scammers and corrupt Chinese officials have turned to Hong Kong to try to hide their money offshore.

But even when used legally, offshore companies can make it harder to sniff out crime.

Local shareholder activist David Webb said three-quarters of companies listed in Hong Kong are incorporated in the Cayman Islands or Bermuda.

Webb also noted that stock exchange rules do not require listed companies to say who owns any British Virgin Islands companies they make acquisitions from, thereby fostering fraud and corruption.

"I don't think there is any appetite in the stock exchange to look under that particular rock, because they'll find snakes if they do," he said. "They see tighter regulation as a problem."

An exchange spokesman said all companies have to comply with the law and exchange rules, and those incorporated in China and Hong Kong count for more than half of the exchange's market capitalisation.

Despite the controversy, few expect authorities in Hong Kong or Singapore to change their regulations surrounding offshore dealings any time soon given how lucrative the industry is.

And, because the cities' own laws haven't been broken, experts say even international efforts to stop tax cheats are unlikely to make any difference.

"If anything, this is going to make people even more careful when they set up offshore holdings," said Clark.

"People will make sure investments are structured in such a way that if they are ever revealed, you won't be in trouble."

Hong Kong authorities said they were aware of the Panama Papers allegations. Singapore's monetary authority said it was investigating and "will not hesitate to take firm action" against wrongdoers.