Mouhcine Fikri, 31, was crushed to death on Friday in the truck in the northern city of Al-Hoceima as he reportedly tried to protest against a municipal worker seizing and destroying his wares.
An image of his inert body - head and arm sticking out from under the lorry's crushing mechanism - went viral on social media, sparking calls for protests nationwide including in the capital Rabat.
Footage online showed thousands of people following the yellow ambulance that carried Fikri's body through Al-Hoceima in the ethnically Berber Rif region on Sunday.
Interior Minister Mohamed Hassad condemned the incident and vowed that an investigation would be held to "determine the exact circumstances of the tragedy and punish those responsible".
"No one had the right to treat him like this.... We cannot accept officials acting in haste, anger or in conditions that do not respect people's rights," he told AFP.
The funeral procession was led by a dozen drivers in their cars - including taxis - and marchers waving Berber flags.
The ambulance headed to the area of Imzouren some 20 kilometres (12 miles) southeast of the city, where Fikri was buried in the late afternoon.
The circumstances of his death remained unclear.
Moroccans angered by the death of the fisherman Mohcine Fikri, crushed to death in a city garbage truck Hoceima, northern Morocco. Source: EPA
But a human rights activist told AFP that the authorities forced the fishmonger to destroy several boxes of swordfish. Catching swordfish using driftnets is illegal.
"The goods were worth a lot of money," said Fassal Aoussar from the local branch of the Moroccan Association of Human Rights (AMDH).
"The salesman threw himself in after his fish and was crushed by the machine," he said.
"The whole of the Rif is in shock and boiling over."
'Criminals, assassins, terrorists!'
Long neglected under the father of the current king, the Rif was at the heart of Morocco's protest movement for change in 2011, dubbed the February 20 movement.
Protests continued in Al-Hoceima late Sunday, an AFP reporter said, with protesters shouting: "Criminals, assassins, terrorists!"
"The people of the Rif won't be humiliated!"
The crowd eventually dispersed around 2130 GMT without incident.
Thousands of demonstrators - including activists for Berber rights - also gathered in Rabat, chanting "We are all Mouhcine!".
Smaller protests were held in several other Rif towns and, unusually, in Casablanca and Marrakesh.
In a statement on Sunday, the AMDH condemned the state for "having trampled on the dignity of citizens since the ferocious repression of the February 20 movement and keeping the region in a state of tension".
It warned of a "possible repeat" of the 2011 protests in the Rif, just a week before Morocco starts hosting international climate talks.
King Mohammed VI has ordered a "thorough and exhaustive investigation" into Fikri's death and the "prosecution of whoever is found responsible", an interior ministry statement said.
The king - who was in Zanzibar on a tour of East Africa - sent the interior minister to "present his condolences" to Fikri's family, it said.
It was the self-immolation of a street vendor in Tunisia in late 2010 in protest at police harassment that sparked Tunisia's revolution and the Arab Spring uprisings across the rest of the region the next year.
Morocco is due to host the COP22 climate talks in Marrakesh from November 7 to 18.
