New Delhi (CNN Business) Just two years ago, India's huge car market was booming and global players were rushing to invest. Now it's been slammed into reverse.

Sales of passenger vehicles plunged 31% in July, according to figures released by the Society of Indian Automobile Manufacturers (SIAM) on Tuesday. It's the ninth straight month of declines and the sharpest one-month drop in more than 18 years, SIAM Director General Vishnu Mathur told CNN Business.

"This is a very deep sort of a slump that is impacting every segment of the industry," Mathur said.

India had been a bright spot for carmakers until recently, with annual sales of passenger vehicles rising by about 33% over the past five years.

Big global players like Hyundai and its subsidiary Kia have invested billions to expand their footprint in the country, and new players like Chinese state-run carmaker SAIC have also tried to grab a slice of business.