NEW YORK (REUTERS) - US regulators will get access to Chinese companies' audit documents under a deal announced on Friday, opening the way to probes of bungled audits after a two-year stand-off between China and the United States.

The nonbinding deal is only a partial victory for the United States, which has been blocked from investigating accounting scandals at dozens of Chinese companies listed on US stock exchanges.

It applies only to enforcement cases against auditors, not against China-based companies suspected of accounting fraud. And it does not allow US regulators to do on-the-ground inspections of auditors in China - a key part of efforts to combat fraud.

"This is a step in the right direction," said James Doty, chairman of the Public Company Accounting Oversight Board, the US regulator for audit firms.

The agreement does not replace the need for the PCAOB to inspect audit firms in China, he said.

Effective on May 10, the pact calls for the PCAOB to cooperate with its counterparts in China, the China Securities Regulatory Commission (CSRC) and the Ministry of Finance, on the exchange of documents.

Any nonpublic documents exchanged will be kept confidential, according to a memorandum of understanding between the agencies.

The signing of the memorandum "is a significant step in China-US audit oversight" and paves the way for cross-border enforcement assistance between the two countries, the CSRC said in a statement.

Investors have lost billions of dollars on Chinese companies selling shares on US exchanges in accounting scandals since 2010. Many of those companies have been booted from US exchanges, but hundreds still have shares trading in the United States.

The deal may not resolve a lawsuit filed by the US.

Securities and Exchange Commission against five top audit firms in China over their refusal to turn over documents.

Under Friday's agreement, the PCAOB can share documents with the SEC, but only if they were obtained for a PCAOB enforcement action.

The SEC in December charged the Chinese affiliates of accounting firms Deloitte, KPMG, PricewaterhouseCoopers , BDO and Ernst & Young with securities violations for their refusal to produce audit papers.

The firms said that turning over the papers would put them in violation of China's state secrets law.

The PCAOB has been negotiating with China for more than two years to get access to documents and permission to do joint inspections with the Chinese.

China resisted out of concern about exposing state secrets, triggering a high-stakes standoff and raising the risk that China-based auditors would be deregistered by the PCAOB.

That in turn could have triggered massive stock exchange delistings of China-based companies, which have to file audited financial statements to meet exchange requirements.

Scores of US-based multinational companies would also have lost their ability to get their operations in China audited.

The deregistration of China-based auditors is not yet off the table, because they have to be inspected to have the right to audit US companies, Mr Doty said.

Negotiations are continuing with China over joint inspections, he said.

Friday's agreement represents an important change in the stance of Chinese authorities, Mr Doty said. They likely realized they need to be more transparent to have access to international capital markets, he said.

"There were a lot of people who saw the unworkability of the position in China that any kind of information or access to work papers was somehow a breach of national security," Mr Doty said. "A lot people said that's just nonsense - no one believes that."