The longest-serving mayor in Boston history told voters on Thursday that he would not seek a sixth term in office, setting the stage for the city's most competitive mayoral race in decades.

Mayor Tom Menino, 70, declared his intention not to seek reelection to the office he has held since 1993 at Boston's historic Fanueil Hall.

"I never dreamed I would end up here, mayor of Boston, during its best years," said Menino, who was hospitalized for a month last year after falling ill while on vacation in Italy.