“It’s not so much that China is more active but that Australia is more receptive in some respects and more vulnerable,” said John Fitzgerald, a professor at Swinburne University of Technology in Melbourne, Australia, who studies civil society in China.

Concern about the influence of Chinese money has been building for years and erupted again with new disclosures about the two businessmen, both billionaire property developers: Chau Chak Wing, an Australian citizen, and Huang Xiangmo, a resident who has applied for citizenship.

Duncan Lewis, the director of the Australian Security Intelligence Organization, warned leading political parties two years ago against accepting contributions from the men because of their ties to the Chinese government, according to a joint report by Fairfax Media newspapers and “Four Corners,” a current affairs television program.

But the Liberal Party and its governing coalition partners, as well as the opposition Labor Party, continued to take the money. The news organizations found that the men and their associates had made at least $5 million in political donations in Australia in recent years, including more than $820,000 since Mr. Lewis’s warning.

The most striking disclosure, though, revolves around a donation that did not occur. As a general election approached last year, Mr. Huang pledged to give an additional $300,000 to the Labor Party. But weeks before the vote, the report said, he rescinded the offer and made clear why: He was upset about a party official saying Australia should send naval patrols to challenge Beijing’s claims to the South China Sea.

The Pentagon has urged Australia to join it on such patrols, but the government has resisted.

On Tuesday, Prime Minister Malcolm Turnbull said he was preparing legislation to ban foreign political donations. “Just as modern China was based on an assertion of national sovereignty, so China should always respect the sovereignty of other nations, including our own,” he said.