Aviva, Britain's largest insurer by assets, is looking out for default red flags as Beijing's crackdown on shadow banking collides with the heaviest debt repayment schedule in more than two years this month. Borrowers from the world's second-largest economy have the equivalent of US$112 billion of all types of bonds maturing this month, the most since April 2011. Mainland firms account for eight of the 10 financially weakest issuers of US dollar-denominated notes in Asia outside Japan, according to a Standard Chartered report on profitability, leverage and capital structure dated July 5. "It's important to look at your portfolio and decide whether the corporates in which you hold positions have any financing vulnerabilities," said Tim Jagger, a Singapore-based fixed-income portfolio manager at Aviva Investors Asia, a unit of Aviva. "If they are highly dependent on bank debt or trust financing, which is obviously an area that is receiving the authorities' attention, that's an obvious red flag." Shipbuilder China Rongsheng Heavy Industries is seeking financial help from the government, three months after Suntech Power defaulted on US-dollar bonds. Slowing economic growth and government efforts to curb risky lending are exacerbating refinancing difficulties amid soaring bond yields. Average US-dollar debt costs have risen 0.76 percentage point to 6.28 per cent since the end of May, according to JP Morgan Chase indices. An additional US$110 billion of notes sold by mainland borrowers are due by the end of August. Some 77 per cent of bonds maturing this month and 99 per cent of notes maturing next month remain outstanding. Mainland firms are the second-most indebted in the region, after Hong Kong's, figures in Standard Chartered's report on debt as a percentage of gross domestic product show. "Sectors such as coke and coal mining and steel manufacturing are blighted by huge overcapacity," Jagger said. "It's hard to see how the fundamentals of those sectors will improve any time soon." The State Council, led by Premier Li Keqiang, wants money allocated to transform the structure of the economy to focus more on domestic consumption. Money-market rates leapt to the highest level in June since at least 2003, as Li tried to rein in shadow lending. The cash crunch has added to concerns some companies may be unable to pay off debts as growth cools.