China"s tech hub of Shenzhen aims to make it harder for people from out-of-town to settle in a rare tightening of residency rules, as its population balloons and resources and services come under pressure. While the southern boomtown is far from being China"s most populous city, its population grew by 7.1 million in the past decade to 17.56 million in 2020, with the jump surpassing increases in entire provinces such as Jiangsu and Shandong over the same period. The number overshot a 14.8 million target set in 2016 for 2020. The city"s population growth is being propelled by its thriving tech industry, loose urban residency curbs and generous home purchase subsidies. The educational threshold for incoming people seeking a residency permit, the so-called hukou, will be raised and requirements for getting a permit through marriage will also be tightened, according to draft revisions on the rules posted on the website of Shenzhen justice bureau on Tuesday. The revisions are expected to close some loopholes that allow people from out of town to make speculative home purchases through sham marriages or lax talent policies. read more Hukou permits have been used to control internal migration in China since the 1950s. When introduced, they were mainly aimed at rural folk seeking work in cities to prevent them from overwhelming urban resources. A hukou also allows one to buy a home in that city. Certain categories of outsiders who work in Shenzhen can apply for a hukou after five years, but that will be doubled to 10 years, according to the draft revisions. The population boom in recent years has lit up the city"s property market and put big pressure on resources and services such as schools. read more Shenzhen"s housing market has soared since last year despite already sky-rocketing home prices, fuelled by rampant borrowing, the migration influx and tight housing supply.