The US Open was plunged into chaos on Thursday after environmental activists disrupted play, forcing a 49-minute stoppage as the tennis showpiece became the latest high-profile sporting event to be targeted by protesters.

The semi-final clash between American teenager Coco Gauff and Karolina Muchova in the Arthur Ashe Stadium was halted in game two of the second set as four protesters wearing t-shirts with the slogan "end fossil fuels" began chanting the same message.

The protesters, from the environmental campaign group Extinction Rebellion (XR), were greeted with jeers and chants of "kick them out" by other spectators as security staff moved in.

One of the protesters glued his feet to the concrete floor of the stadium, preventing his swift removal from the arena, tournament officials said.

The drama unfolded as Muchova prepared to serve early in the second set with Gauff leading 6-4, 1-0 just after 8pm local time.

Gauff and Muchova waited patiently on the court for several minutes but eventually left the court to return to the locker rooms.

The US Tennis Association said in a statement: "Three of the four protesters were escorted out of the stadium without further incident. The fourth protester affixed their bare feet to the floor of the seating bowl," the statement added.

"Due to the nature of this action, NYPD and medical personnel were needed in order to safely remove this individual from the stadium."

The USTA said all four spectators had been taken into police custody.

Television footage showed Gauff and Muchova trying to stay loose in the locker rooms, consulting with coaching staff during the unprecedented delay.

Gauff and Muchova finally returned to the court at around 8.50pm EST after a stoppage in play officially timed at 49 minutes. Gauff, 19, would go on to win in straight sets 6-4, 7-5. (AFP)