New Bedford Police Chief David A. Provencher, who served on the force for 35 years, died Sunday night, officials said.
The death was unexpected, said Elizabeth Treadup Pio, said a spokeswoman for New Bedford Mayor Jon Mitchell.
Provencher, 59, had been chief for five years, Pio said.
He died around 7:30 p.m. at St. Luke's Hospital in New Bedford from respiratory arrest, the mayor said in a statement.
"Tonight the city of New Bedford lost an outstanding police chief and a great man," Mitchell said in the statement. "Our prayers go out to Dave's family. We will do everything in our power to support them at this most difficult time."
The mayor added, "Chief Provencher leaves behind a legacy of a more modern and effective police department and a stronger New Bedford community. I am shocked and saddened by his passing. I will miss him as a colleague and friend."
Bristol County District Attorney Thomas M. Quinn also mourned Provencher's death.
"Chief Provencher was a great ally, a consummate professional and a faithful public servant," Quinn said in a statement. "He devoted his life to the people of New Bedford and always had the community's best interests in his heart. He will be sorely missed by all of us at the district attorney's office."
Other officials took to Twitter to express their condolences.
Steven Martins, a New Bedford city councillor, tweeted, "Chief Provencher dedicated his life to serve and protect us. He was a great friend. My heart is broken."
Provencher leaves behind two sons. Funeral arrangements have not been announced.
Aneri Pattani can be reached at aneri.pattani@globe.com. Follow her on Twitter @apattani95.