BEIJING—China’s economic growth decelerated to its slowest pace in decades, weakened by trade tensions with the U.S. and businesses that held back from making big investments despite encouragement from Beijing.

The economy grew by 6.2% in the second quarter, down from 6.4% in the period before, official statistics showed Monday. Growth was slower than the 6.3% year-over-year rate forecast by economists.

Investments...