United States Vice-President Joe Biden, who is visiting China, has said the US would never default on its debt.

In a speech on the last day of his visit, he reiterated that China's large holdings of dollar assets were safe.

His trip comes amid mounting tension between the two over America's debt.

Chinese officials have criticised the political row in the US over raising its borrowing ceiling, and expressed concern over the recent downgrade of the country's credit rating.

"You're safe," Mr Biden told university students in the south-western town of Chengdua, in answer to a question about Washington's ability to repay its debt.