A Chinese airline that offers six-hour flights taking passengers between two cities via an out-of-the-way airport in a third city has been deemed the most-exhausting airline.

Okair, a private airline in Beijing, confirmed it has started a flight that stops in Haikou, on the southern island province of Hainan, while taking passengers back and forth between Nanjing, capital of Jiangsu province, and Tianjin, Modern Express reported.

The flights are mainly meant to accommodate passengers going from Nanjing to Haikou and Haikou to Tianjin, or vice versa.

"No tickets will be sold to passengers who fly from Nanjing to Tianjin," said Gan Wei, marketing manager for the airline.

The distance between Nanjing and Haikou is about 1,990 km and it is 2,370 km between Haikou and Tianjin. From Nanjing to Tianjin, in contrast, the distance is only 907 km, which can be traveled on a one-hour direct flight.

Four of the flights are scheduled every week.