Prime Minister Pedro Sanchez and Catalonia's separatist president Quim Torra also said their goodbyes to Caballé, who died on Saturday aged 85.
Hailed as one of the greatest singers for her vocal virtuosity and dramatic powers, Caballé charmed audiences for half a century with a huge repertoire that saw her perform across the globe.
Nicknamed “la superba” in her native Spain, she was propelled into the mainstream when her duet with Freddie Mercury, a boundary-busting combination of opera and rock, became the anthem for the 1992 Olympic Games in Barcelona.
“For me, Montserrat was the greatest soprano in the 20th century,” Carreras told reporters.
“The only person who could get close was Maria Callas.”
Greek composer Vangelis, with whom Caballé collaborated, sent a wreath with the message: “For the one and only Montserrat Caballé”.
Born in April 1933 to a humble Barcelona family, Caballé was buried next to her parents in the city's Sant Andreu cemetery in a northern working-class district.
A wreath hangs from the hearse carrying the remains of Spanish opera singer Montserrat Caballe during her funeral in Barcelona on October 8th.
Bernabe Martinez (2L) walks past the hearse carrying the remains of his wife Spanish opera singer Montserrat Caballe
Former queen of Spain, Sofia (R) listens to Spanish prime minister Pedro Sanchez (2R) beside Catalan regional president Quim Torra (3R), Spanish minister of culture and sports Jose Guirao (4R), leader of People's Party PP, Pablo Casado (4L) and mayor of Barcelona Ada Colau (3L) during the funeral.
Spanish tenor Jose Carreras talks to journalists during the funeral.
Spanish prime minister Pedro Sanchez shakes hands with former queen of Spain, Sofia,
Venezuelan music critic and biographer of opera singer Montserrat Caballe, Roger Alier i Aixala
Catalan regional president Quim Torra looks on as PM Pedro Sanchez talks to Queen Sofia during the funeral.
Mayor of Barcelona Ada Colau (L) arrives to attend the funeral.
Representatives of Ciudadanos (Citizens) political party, Ines Arrimadas (L) and Juan Carlos Girauta arrive at the funeral.
Italian recording artist, actor, and winemaker Albano Carrisi, better known as Al Bano was also in attendance.
Former Catalonia's regional president Jordi Pujol leaves a funeral parlour in Barcelona after visiting the wake of Spanish Catalan world-famous opera singer Montserrat Caballe
Montse Caballe, the niece and personal secretary of the Spanish Catalan world-famous opera singer stands at the entrance of the funeral parlour in Barcelona where her aunt's wake was held, on October 7th.
And the reason we will always remember the greatest diva in the world: