Apartment complexes are seen in Seoul's Gangnam District, Monday. Yonhap

"I found a 1.1 billion won ($737,000) apartment I wanted to buy and planned to finance 450 million won with a mortgage. But my entire plan has fallen apart now that banks are suddenly tightening mortgage lending," one user wrote on a Naver real estate community.

"I had planned to buy a home using my savings and a mortgage of up to 600 million won. But after KB Kookmin Bank cut its mortgage lending cap to 300 million won last week, I had no choice but to abandon the plan," another user wrote.

Similar complaints have spread across online communities in recent days as major lenders tighten household lending, making it increasingly difficult for prospective homebuyers to secure mortgages.

The country's five largest lenders — KB Kookmin, Shinhan, Hana, Woori and NH NongHyup — have begun tightening mortgage rules after approaching their annual household lending growth targets set by financial authorities.