SYDNEY, Australia — Prime Minister Scott Morrison of Australia was blindsided by reports that a state government had quietly sidestepped federal regulators and signed a deal with China to participate in that country’s contentious Belt and Road infrastructure initiative.

Mr. Morrison said this week that the agreement, signed last month between the governments of China and the state of Victoria, undermined the federal government’s ability to conduct foreign policy at a time when intelligence officials are concerned that China is trying to exert undue influence in Australia.

Mr. Morrison told reporters he was “surprised” that the Victorian government would involve itself in a “matter of international relations” without discussing it first.

“They know full well our policy on those issues and I thought that was not a very cooperative or helpful way to do things on such issues,” Mr. Morrison said.