(basically people migrate mainly for  economic opportunities) (The chinese coastal areas were not the early COVID19 hot spots )

Sichuan and guangdong provinces in 2018 had popn of respectively 83 millions and 113 millions https://www.statista.com/statistics/279013/population-in-china-by-region/

But during the 80s, Sichuan and guangdong provinces had popn of respectively >100 millions and about 60 millions(china popn increased by a 1/3 since 1985); both the Sichuan decrease(through outbound migration) and guangdong increase(inbound migration)  have been drastic. Mind you sure guangdong &coastal provinces/cities have hier than average income/capita, sichuan's is till 80% of national average. https://en.wikipedia.org/wiki/List_of_Chinese_administrative_divisions_by_population

https://en.wikipedia.org/wiki/List_of_Chinese_administrative_divisions_by_GDP_per_capita

Most of the internal migrants in hindustan came from Uttar pradesh, bihar.. to destination like new dehli ... Seems the natural popn growth of such hindu belt states are hier than figures indicated below bcos of outbound migration. New dehli is one of the covid hotspots there

https://www.weforum.org/agenda/2017/10/india-has-139-million-internal-migrants-we-must-not-forget-them/

 https://www.livemint.com/news/india/lockdown-impact-over-41-lakh-migrant-workers-return-to-uttar-pradesh-bihar-11592800284093.html

https://scroll.in/latest/963544/covid-19-bihar-says-it-will-not-test-returning-migrant-workers-or-send-them-to-quarantine

Unlike Sichuan, Hindu states like Uttar pradesh, Bihar keep their popn growing fast. Uttar Pradesh popn density has reached 1000/sq km in 2020 while Bihar has exceeded that quite some years ago; fabulous demografic dividends, what else...