WASHINGTON, March 14 (Xinhua) -- As China and the United States marked their 40th anniversary of diplomatic relationship this year, the history of China-U.S. sister city ties also hit its 40-year milestone.

Sister city ties between China and the United States began shortly after the two countries established diplomatic relationship in 1979. The Chinese province of Hubei and the U.S. state of Ohio became the first pair of sister province/state, while the Chinese city of Nanjing and the U.S. city of St. Louis became the first pair of sister cities.

Forty years on, bilateral sister city relationship has grown and flourished, now the two countries enjoy 277 pairs of sister relationship at different levels such as sister counties, ports and schools, and the momentum is still going strong, according to Sister City International (SCI) President Roger-Mark De Souza.

While traditionally sister city relationship focused on cultural exchanges, tourism, and commerce, it has expanded in scope as China-U.S. relationship deepened, bringing Chinese and U.S. cities together on issues such as disaster mitigation, sustainable development, cyber security and sports.

Below are some notable milestones in the China-U.S. sister city relationship.

-In 1979, the Chinese city of Nanjing and the U.S. city of St. Louis became the first pair of sister cities between the two countries while the Chinese province of Hubei and the U.S. state of Ohio became the first pair of sister province/state. In 2009, leaders of Hubei province and Ohio renewed their sister province/state agreement. Ohio is also sister province/state with Taiwan province.

-In 1981, the Chinese city of Guangzhou became sister cities with the U.S. city of Los Angeles, which is also a sister city of Taipei.

-In 1984, Beijing and Washington, D.C. became sister cities, marking the beginning of the relationship between the two countries' capital cities. Earlier in 1980, Beijing became sister cities with New York City.

-In 1985, the Chinese cities of Shanghai and Shenyang became sister cities with the U.S. city of Chicago, making China the only country where Chicago has more than one sister city.

-In 1986, the Chinese city of Shenzhen became sister cities with the U.S. city of Houston, which is also a sister city of Taipei.

-In 2014, the Chinese People's Association for Friendship with Foreign Countries and SCI jointly hosted the first U.S.-China Sister Cities Conference in Washington, D.C., featuring three days of activities with more than 400 community leaders, citizen diplomats, business executives, educators, mayors, provincial leaders, and municipal officials from China and the United States joining together to discuss strategies on how to grow and strengthen exchanges and business ties at the sub-national level.