Adams, 25, played for Mamelodi Sundowns in the South African league, helping them to the African Champions League title in the 2025/26 season.
No cause of death has yet been confirmed.
He started the World Cup fixtures against Mexico and Czech Republic, and came off the bench in the 1-0 win over South Korea that earned Bafana Bafana a first ever place in the knockout rounds of the global finals, where they were knocked out by Canada.
"This passing has ripped everybody apart, returning from the World Cup and then to get such news," Brendine Johnson, Adams' mentor, told Soccer Laduma.
"I had a close conversation with him on Thursday. The guy was really positive on returning back, and being able to return after the World Cup, knowing what lies ahead. He was prepared."
South Africa's minister of sport Gayton McKenzie also expressed his condolences.
"Our nation mourns alongside his family, his teammates and the millions of supporters who watched him grow from a promising academy prospect into a full Bafana Bafana international," McKenzie said in a statement.
FIFA president Gianni Infantino offered his condolences via Instagram, saying his "thoughts and condolences, as well as those of everyone at FIFA and the global football community, are with his family, friends and teammates".
Adams came through the youth development structures at Stellenbosch FC and joined Sundowns in January 2025.
He made his international debut against Mozambique in 2022 and won 13 caps, scoring two goals, both in qualifiers for the current World Cup.