NEW YORK -- The US Open semifinal between Coco Gauff and Karolina Muchova was delayed by 49 minutes because of a disruption by four environmental activists in the Arthur Ashe Stadium stands Thursday night. One protester glued his bare feet to the concrete floor.

Gauff was ahead 6-4, 1-0 when play was halted early in the second set.

Security guards and, later, more than a half-dozen police officers went over to confront the protesters, who were wearing shirts that read, "End Fossil Fuels." Three of the activists were escorted out within several minutes, but it took longer to remove the person who stuck his feet to the ground. One protestor said they wanted the US Open to be accountable because it has sponsors who are large corporations whose policies are contributing to global warming.

All four protesters were taken into New York Police Department custody, according to the United States Tennis Association.

Spectators were asked to move away to clear a path for the police, who were cheered by fans sitting near the section where the disruption happened.

Gauff sat on her sideline bench for a bit during the break in the match, eating fruit out of a plastic container, before hitting a few practice serves. Muchova was briefly visited by a trainer during the interruption.

Later, both players headed toward the locker room as the delay continued. Gauff sat on a treadmill, a towel draped over her lap, while chatting with members of her team.

It is the latest in a recent series of protests at sporting events -- and tennis, in particular -- related to the use of fossil fuels.

At Wimbledon in July, two matches were interrupted when environmental activists jumped out of the stands at Court 18 and scattered orange confetti on the grass.

At a US Open tuneup tournament in Washington, D.C., last month, about a dozen people were asked to leave the site after chanting and displaying signs protesting the use of fossil fuels.

Gauff, a 19-year-old American, and Muchova, a 27-year-old from the Czech Republic, were both playing in the semifinals at Flushing Meadows for the first time. Gauff ended up winning 6-4, 7-5.

Their match was the first of the evening. The other women's semifinal, between Aryna Sabalenka of Belarus and Madison Keys of the United States, was later Thursday night.

The two winners will play each other for the women's singles championship in Ashe on Saturday.

Information from The Associated Press was used in this report.