A key gauge of China's debt has topped 300% of gross domestic product, according to the Institute of International Finance (IIF), as Beijing steps up support for the cooling economy while trying to contain financial risks.

China's total corporate, household and government debt rose to 303% of GDP in the first quarter of 2019, from 297% in the same period a year earlier, the IIF said in a report, which highlighted rising debt levels worldwide.

"While authorities' efforts to curb shadow bank lending (particularly to smaller companies) have prompted a cutback in non-financial corporate debt, net borrowing in other sectors has brought China's total debt to over $40 trillion - some 15% of all global debt," the report said.

"Of note, onshore bond issuance suggests a big pickup in borrowing by local governments and banks this year."