'sea gate', Qihai dialect: [haɪ.məŋ], Shanghai: [hɛ̝.məŋ]) is a district of Nantong, Jiangsu province, with a population of approximately 1 million.

It is located at the opposite side of the Yangtze River to Shanghai and is directly north of Chongming Island except for a small portion that forms Haimen District's Haiyong Town.

Haimen is located in the poorer north Jiangsu region and, together with Qidong City, has long had one of the highest rates of liver cancer in China and in the world; over one in ten adults in the rural areas died from liver cancer c.1970, with mortality halving since then with improvements to drinking water and food.

Several sandbanks, including Dongzhou (东洲; 東洲) and Buzhou (布洲), joined with the mainland in the Tang dynasty.

[8] Because the mouth of the Yangtze River moved northward during the Ming dynasty, Haimen has dealt with flooding that destroyed parts of the county, including Lüsi (吕四; 呂四), Yudong (余东; 余東), and Sijia (Chinese: 四甲).

[7] In 1672, under the Kangxi Emperor of the Qing dynasty, the seat moved to Jinghai Township (静海乡; 靜海鄉).

In 1768, the county became an independent subprefecture with the seat moving to Maojia Town (茅家镇; 茅家鎮).