The groups behind a new China-based ratings firm said Wednesday they planned to break the dominance of US agencies in assessing state and company debt, a much-criticised part of the financial system.

China's Dagong, Egan-Jones Ratings (EJR) of the United States and RusRating in Russia are to set up a joint venture within six months to be headquartered in Hong Kong, the companies said at a news conference unveiling the partnership.

The three partners are inviting "organisations from every country" to join Universal Credit Rating Group, and Dagong chairman Guan Jianzhong said dozens of companies from more than 20 countries have expressed an interest.

The new group is hoping to break the stranglehold of US-based Fitch, Standard & Poor's and Moody's, which provide vital risk assessments to investors about debt instruments, in the next five years.

"I believe we can do this. Our goal is to form a new system with the synergy of everybody that will balance the existing system," Guan said.

The global financial crisis proved that the current international ratings system has flaws that "jeopardise human prosperity and development" and needs to be reformed, the firms said in a document they dubbed the "Beijing Declaration".

"We live in a very complex world -- there are many competing interests and cultural view points," Richard Hainsworth, president of RusRating, said at the briefing.

"It is not sufficient in such a world for an industry as critical as credit rating to be dominated by just a tiny number of companies."

Inflated ratings issued by "some of the firms in the United States" paid by the issuers played a primary role in causing the 2008-09 financial collapse and the excesses have continued due to a lack of curbs, said EJR President Sean Egan.

"It's obvious that the supervision of the rating agencies to date has fallen far short of the mark," he said.

"It's been rather geocentric and it's time to get on an even playing field and... we hope that will happen in the future with the efforts of today," he added.

Fitch, S&P and Moody's were widely criticised for having given their highest ratings to the debt instruments whose failure sparked the crisis in Western banks in 2008.

The power of Fitch, S&P and Moody's has also drawn the ire of European officials amid the continent's debt crisis, though talk of creating Europe's own rating agency was ruled out amid concerns about costs and objectivity.

Universal Credit Rating Group will be "independent" and composed of private firms "whose responsibilities do not conflict with credit rating, and which do not represent the interest of any particular country or group", the companies said.

The big three US agencies will not be considered for membership "because there is big divergence between the principles and positions we respectively follow", said Guan.

Dagong in August 2011 lowered its main rating for US sovereign debt from A+ to A, with a negative outlook, after Congress passed new legislation to raise Washington's debt ceiling.

Meanwhile, it maintained China's local and foreign currency rating at AA+ and AAA respectively, with a stable outlook. AAA is its highest rating.

S&P, also in August last year, slapped the US with a credit downgrade -- cutting it one notch to AA+ -- citing political deadlock over the deficit.

Egan-Jones Ratings serves institutional investors and was granted status as a "nationally recognised statistical rating organisation" by the US Securities and Exchange Commission in late 2007.

RusRating, based in Moscow, focuses on ratings for the banking sector.