Bond markets are growing riskier as investors seeking steady returns bid up prices and ignore some early warning signs similar to those that flashed during the credit bubble.

Last week, prices on high-yield, or junk, bonds hit their highest level since 2007, nearly double their lows of the credit crisis. Nine months into the year, companies have sold $172 billion in junk bonds, already an annual record, according to data provider Dealogic.

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