Aluminum Corp of China, or Chinalco, signed loan agreements on Friday with four Chinese banks to fund its $US19.5 billion ($A27.69 billion) investment in mining giant Rio Tinto, Chinese state media said. The state-run Bank of China (BOC) was one of the four, state news agency Xinhua said, quoting BOC, with the agreements totalling $US21 billion ($A29.82 billion) in syndicated loans. Xinhua's report did not say which other banks were involved. But Caijing magazine earlier reported the other lenders were state-run Agricultural Bank of China, and two policy lenders which work exclusively on government-assigned projects - China Development Bank and Export-Import Bank of China. Australia's competition watchdog said on Wednesday it would not block Chinalco's investment in Rio Tinto.