Answered by ZUPAN | Nov. 06, 2019 12:26
To be eligible for 144 hour visa free transit within Guangdong province, you will have to book a ferry or a train ticket in advance, before your departure from Hanoi. In reality, the buses are also eligible, but just in theory because you simply cannot book a bus ticket from Shenzhen to Guangzhou online in advance! You will have to choose among a ferry from Shenzhen Shekou or Guangzhou Nansha ports to Hong Hong or a train from, be careful, Guangzhou East to Hong Kong Hung Hom railway station. You should book your ferry ticket through CKS - Chu Kong Passenger transport company website and a train through this, China Travel Guide website. Anyway, you should have in mind that a train ticket has to be booked at least 7 - 8 days before your intended travel by train from Guangzhou.
In the end... It is allowed to fly from Guangzhou to Hong Kong by direct flight, but this option is undoubtedly the most expensive, so the least popular among other options.