A team of American humanoid robots has defeated rivals from Iran in the final of an annual football tournament for intelligent sporting machines held in China.

In a tightly fought final, a team designed by the University of Pennsylvania and named THORwIn scored five goals compared to four from Iranian team Baset Adult-Size, organisers said on Wednesday.

The game was the final of the largest "adult" size category in the Robocup, an annual event held this year in the eastern Chinese city of Hefei.

Video: Robots playing soccer. RoboCup, the World Cup for robots, is being held in the central Chinese city of Hefei. https://t.co/zWIbJcgQln — China Xinhua News (@XHNews) July 22, 2015

The annual Robocup is seen by some scientists as a way to help promote the cause of designing machines capable of carrying out more complex tasks.

The robots are not human-controlled and play football in a manner resembling young children: swarming around the ball, kicking haphazardly and often falling over.

Iran has emerged as an unlikely force in the world of robot soccer in recent years, and last year the finals were held in Tehran.

The Robocup saw machines competing in a variety of categories depending on their size.

A total of 175 robot teams from 47 different countries and regions took part in this year's event, according to the China Daily newspaper.