Indian traveller to Hongkong, Macau

No, unfortunately, this is not possible. The only possible way how to enjoy 24 hour visa free transit when traveling from Hong Kong/Macau to entire Guangdong province is by entering the province by air. Overland crossings are not eligible for 24 hour visa free transit. Also, if you enter Guangdong province by air, you will have to leave it to some other territory/country within 24 hours without returning to Hong Kong.

But the article above says you can enter mainland by train or sea in addition to air travel.
Also there are proper immigration channels available before and after boarding bullet train from Hongkong and similarly before and after boarding ferry from Shekou to Macau.

Apoorv, this is correct in certain Chinese transit areas, but this is not the case in Guangdong province because of the specific status of Hong Kong and Macau Special Autonomous Regions. So, if you want to enter Guangdong province (where Shenzhen is located), under 24 or any other visa free transit scheme, you are allowed only to do that by air. In other words, you can fly from any country or even Hong Kong to three airports in Guangdong: Shenzhen, Guangzhou and Jieyang Chaoshan airports. By the way, high speed train was never eligible for any kind of visa free transit and even not for visa on arrival scheme because both Hong Kong and mainland China border controls are located at West Kowloon station in Hong Kong.

I understand that many find this as an obstacle, but this is the reality.