A campaign by Chinese authorities to encourage people to replace their old apartments with new ones is attracting interest, but faces one major hurdle: the participants in the program are struggling to sell their current homes.

Flagged at a key political meeting last month, the campaign is meant to help cities across China offload their growing stock of new apartments and provide crucial cash flow to ailing developers. As of May 6, more than 50 cities have launched their own versions of the "swap old for new" program, according to a private survey by China Index Academy.

But analysts, real estate agents and developers say buying interest in second-hand homes is very limited, casting doubt over the success of the campaign and suggesting the property sector downturn in China has further to run.