China is "quite serious about living up to the commitments they have made regarding North Korea," U.S. Commerce Secretary Wilbur Ross said on Wednesday.

The order for mainland lenders to stop doing business with Pyongyang "is a logical next step in the sanctions, and a very important one," he told CNBC's "Squawk Box."

"Chinese commercial banks had been a big route for facilitation of trade to North Korea so the fact that the PBOC has put out a taboo, that's a very big deal," the billionaire said, referring to China's central bank, or the People's Bank of China.

Last week, sources told Reuters that the PBOC had instructed domestic banks to implement United Nations sanctions against the rogue state. The development comes on the heels of Pyongyang's sixth nuclear test earlier this month and follows incessant demands from President Donald Trump for more Chinese action against North Korean leader Kim Jong Un.

On Tuesday, the U.S. Treasury Department announced new sanctions on banks and individuals tied to the isolated nation as part of efforts to cut off financial support for Kim's weapons programs.

The PBOC move was "a gigantic step" and assuming that it's followed through, "that's a very good sign, it's very, very important pressure," said 79-year-old Ross, who made a fortune investing in distressed assets before joining the White House.