Are there nonstop flights from Shenzhen (SZX) to Changsha (CSX)?

Yes. China Southern Airlines fly this route. Flight time is about 1h 14m.

What is the fastest connection from Shenzhen (SZX) to Changsha (CSX)?

via Nanchang ≈ 2h 10m, via Xiamen ≈ 2h 20m, via Zhanjiang ≈ 2h 21m (estimated flying time, excluding layovers).

from 10,000 ANA miles (economy, one way, based on the published award charts).

Shenzhen Bao'an International Airport (SZX) to Changsha Huanghua International Airport (CSX)・620 km

Nonstop flights available (1 airline). Flight time about 1h 14m. Nonstop return flights also operate.

With milesANA 10,000 miles+ (via CKG)Economy, one way, estimate. Tap a connection for miles by cabin.

12 one-stop options, sorted by estimated flying time. Tap one to see the airlines on each leg and booking links.

Times are estimated from distance. Check schedules, frequency and availability with the airline or a booking site.