The Lowy Institute's 2019 Global Diplomacy Index, published Wednesday, showed China had climbed to the top spot for the first time, underlining Beijing's growing international ambitions.
The index is an analysis of the number of embassies and consulates maintained by countries around the world.
The Australian think tank reported China had 276 diplomatic posts worldwide, narrowly ahead of the U.S., which was found to have 273. The two countries were found to have an equal number of embassies, but Beijing has more consulates around the world than Washington.
"It's ascent to the top spot has been rapid," Bonnie Bley, lead researcher from the Lowy Institute, said in the report published Wednesday.
In two years, China was found to have grown its international network by five diplomatic posts, following the opening of seven new missions and the closure of two others.
In 2016, China was in third place worldwide, behind the U.S. and France — but by 2017, the Asian economic powerhouse had moved up to second place, ahead of France.
Over the same time period, the U.S. has increased its missions but only to 273, up from 271.
"China has overtaken the United States to have the largest diplomatic network globally, while U.S. diplomacy has entered a period of limbo," Bley said via Twitter on Wednesday.
The latest annual country ranking shows China ahead of the U.S., France, Japan and Russia, respectively.
In contrast to China's dramatic rise, Taiwan has seen the biggest drop in diplomatic posts in recent years. The Lowy Institute said this has "directly contributed" to China's lead over the U.S.
The island off the coast of China has seen its diplomatic posts drop to 15 in 2019, down from 22 in 2016.
Both China and Taiwan have a policy that they will each only have full diplomatic ties with another country if they do not also have ties with their rival.
An island off the east coast of the world's second-largest economy, Taiwan is self-governed by an elected government — but it is also claimed by China. Beijing has viewed Taiwan as a sovereign territory since a 1949 split amid civil war.
China has "succeeded in picking off a handful of Taiwan's last remaining diplomatic partners," according to the report.
Beijing has opened new embassies in Burkina Faso, the Dominican Republic, El Salvador, the Gambia and Sao Tome and the Principe in recent years — all former diplomatic friends of Taiwan.