A team ambassador, Kersey appeared Tuesday with fellow former Blazers Terry Porter and Brian Grant at a Portland high school in celebration of African American History Month.
"Today we lost an incredible person and one of the most beloved players to ever wear a Trail Blazers uniform," Blazers owner Paul Allen said in a statement. "My thoughts and condolences are with the Kersey family. He will be missed by all of us. It's a terrible loss."
Kersey averaged 10.3 points and 5.5 rebounds in 17 seasons in the NBA with Portland, Golden State, the Los Angeles Lakers, Seattle, San Antonio and Milwaukee. He helped the Blazers reach the NBA Finals in 1990 and 1992, playing alongside Porter, Clyde Drexler, Kevin Duckworth and Buck Williams.
"He was the greatest guy, the nicest friend, teammate and brother. He was loved by everyone. We will all miss him. He just cared so much," Drexler told Comcast SportsNet Northwest. "This is unbelievable."
Kersey had his best season in 1987-88, averaging 19.2 points and 8.3 rebounds. Kersey played in 1,153 regular-season games, also averaging 1.9 assists and 1.2 steals.
The former Longwood University star ranks second on Portland's career games list with 831, third in minutes played at 21,400, second in rebounds with 5,078, third steals with 1,059, and fifth in points with 10,067.
At 6-foot-7 and 215 pounds, "No Mercy" Kersey had a broad smile and a warm manner that made him a fan favorite.
Trail Blazers guard Damian Lillard posted to Twitter: "Spoke to him regularly about life and the ups and downs of a NBA season. Gone too soon, much love!" Others who posted their condolences included Kobe Bryant and Vince Carter.
Kersey retired from basketball in 2001. He was an assistant coach with Milwaukee in 2004-05 under Porter. In addition to serving as a team ambassador, he appeared on Blazers' broadcasts for Comcast SportsNet Northwest.
At Longwood, a Division II school in Farmville, Virginia, Kersey averaged 17 points and 11.3. He was a second-round pick by the Blazers in the 1984 draft.
"The news is so sudden, and we're sure more details will be forthcoming," Blazers President Chris McGowan said. "But it is indeed a sad day for our organization, the city of Portland and the NBA. Jerome will be remembered not only for his incredible contributions on the court, but his tremendous impact in our community."
Kersey lived with wife Teri in Lake Oswego.