They were led by the Democratic Alliance for the Betterment and Progress of Hong Kong but also had the support of the Civic and Liberal parties, which had previously been silent on the issue.

Many who marched from Statue Square to the SAR government headquarters were retirees and the elderly. The marchers said they had invested in the minibonds because they had been assured there was little or no risk.

"I had the impression Hang Seng would guarantee the minibonds," trading company owner Chou Yong said. "Many people here had never heard of Lehman, they definitely did not understand the risk involved, the government should step in and help us."

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Chou's call for government intervention was supported by DAB district councillor Dennis Wong Tat-tung, who said the government should review regulations on bond sales and help investors regain their assets.

Acting Liberal Party chairwoman Miriam Lau Kin-yee called on investors to collect evidence to prove they had been misled.

Democratic Party's legislator-elect Kam Nai-wai said he will take legal action for the elderly who are without relatives. The party will also apply for the Consumer Council's Legal Action Fund for the lawsuits.

One victim claimed a bank staff advised her to forge her son's signature to get US$100,000 (HK$780,000) from his account to invest in the minibonds.

A Financial Services and Treasury Bureau spokesman said the Securities and Futures Commission and Hong Kong Monetary Authority were working with representatives of Lehman Brothers and the banks that sold the minibonds.

He said the authority has called on banks to write to affected investors and update them on the current situation but Civic Party chairwoman Audrey Eu Yuet-mee said so far just one bank had done so. The authority has also opened a hotline - 8100 2314 - to assist investors with complaints.