SHANGHAI, July 14 (Reuters) - Chinese investors dumped banking and real estate stocks on Thursday, fearing the country's property sector woes will start to hit the financial system, as a growing number of homebuyers threaten to stop making mortgage payments to lenders.

Over the past weeks, a rising number of homebuyers have collectively threatened to halt mortgage payments to banks if developers do not resume construction of pre-sold homes, according to official media.

The "stop mortgage repayment" movement has spread to many Chinese provinces, and involves more than 100 property projects, the Securities Times reported on Thursday.

The CSI300 Bank index fell as much as 3.3% in early trading, hitting its lowest level since March 2020.

Chinese developers listed on the mainland and Hong Kong also slumped.

"People are worried this may hurt bank loans and affect others, not-in-trouble projects," said Steven Leung, executive director of institutional sales at brokerage UOB Kay Hian in Hong Kong.

Smaller lenders suffered fierce sell-offs.

China Merchants Bank dropped as much as 6.3%, while Bank of Chengdu lost 5% earlier in the day.

"China's property downturn may finally adversely affect onshore financial institutions after hitting the offshore high-yield dollar bond market," Nomura chief China economist Ting Lu wrote.

"A disorderly deleveraging may not only lead to a credit crunch for developers and massive defaults in offshore dollar bond markets, but also rising non-performing loans for banks, which sit at the centre of China's financial system."

(Reporting by Samuel Shen and Tom Westbrook; Editing by Sherry Jacob-Phillips)