Answered by Borut | Nov. 16, 2023 00:04
No, it is not... Under 144 hour visa free transit you are supposed to stay within the area of Guangdong province. Also, you should use correct terminology. This scheme is 144 and not 72 hours long. 144 hours has replaced 72 hours in Guangdong province years ago and also this is not a visa, but a transit that is visa free so there is no visa of any kind.
If you only had more time, in that case it could have been possible to make a side trip to Hong Kong, but after you have stayed just a minute more than 24 hours in Shenzhen because that would have allowed you to make a journey that would have Hong Kong as your destination:
Barcelona - Shenzhen - Hong Kong
In the case of more time available during the layover, it could have been possible to take a ferry from Shekou port in Shenzhen, but only after 24 hour stay in Shenzhen and to proceed with ferry to Hong Kong. After your stay in Hong Kong you could have returned to Shenzhen by obtaining a Shenzhen 5 days visa in order to catch your flight for some other country, in your case for Seoul.
However, as you can see, you are short with available time and the procedure is relatively complicated even if you have had more time at your disposal. In other words, you are suggested to stay for the above mentioned 26 hours, covered by 144 hour visa free transit, in the area of Guangdong province. In other words, you are not limited just to Shenzhen, but you can also visit Guangzhou if you wish.