Spain's national broadcaster reported that the barrage included a few rocks and other objects and that two bodyguards were treated for injuries. One could be seen with a bloody wound on his forehead.
It was an unprecedented incident for a royal house that carefully crafts an image of monarchs adored by their country of more than 48 million people.
Spanish fury has been unleashed against a state that appears overwhelmed and unable to meet the needs of people used to living under an effective government.
Officials also rushed Prime Minister Pedro Sánchez from the scene soon after his contingent started to walk the mud-covered streets of one of the hardest-hit areas, where over 60 people perished and thousands of lives were shattered. The disaster fueled by climate change killed at least 205 people in eastern Spain.
"Get out! Get out!" and "Killers!" the crowd in the town of Paiporta shouted, among other insults. Bodyguards opened umbrellas to protect the royals and other officials from the tossed muck.
Police had to step in, some officers on horseback, to keep back the crowd of several dozen, some wielding shovels and poles.
Queen Letizia broke into tears sympathetically after speaking to several people, including one woman who wept in her arms. Later, one of the queen's bodyguards had a bloody wound on his forehead and there was a hole in the back window of the prime minister's official car.
But even after being forced to seek protection, King Felipe VI, with flecks of mud on his face, remained calm and made several efforts to speak to individual residents. He insisted on trying to speak with people as he tried to continue his visit. He spoke to several people, patting two young men on their backs and sharing a quick embrace, with mud stains on his black raincoat.
Still, one woman smacked an official car with an umbrella and another kicked it before it sped off.
While far from awakening the passion that the British hold for their royals, Felipe and Letizia's public events are usually greeted by crowds of fans.
The 56-year-old Felipe took the throne when his father, Juan Carlos, abdicated in 2014 after he was tarnished by self-made financial and personal scandals. Felipe immediately cut a new figure, renouncing his personal inheritance and increasing the financial transparency of his royal house. He and the 52-year-old Letizia, a former journalist, dedicate a significant part of their public agenda to cultural and scientific causes.
Visits to sites of national tragedies are also part of the royal duties for monarchs seen as a stabilizing force in a parliamentary monarchy restored following the death of dictator Francisco Franco in 1975.
The king later told regional authorities at the command post of emergency response efforts that they had to give "hope to those affected by the flood and attend to their needs, guaranteeing that the state is there for them."
Public rage over the haphazard management of the crisis has been building. Felipe heard some jeers when he took part in a tribute to the dead of a deadly 2017 terror attack in Barcelona, but that was nothing comparable to Sunday's reception.
The queen had small glops of mud on her hands and arms as she spoke to women.
"We dont have any water," one woman told her.
Many people still don't have drinking water five days after the floods struck. Internet and mobile phone coverage remains patchy. Most people only got power back on Saturday. Stores and supermarkets are in ruins and Paiporta, population 30,000, still has many city blocks completely clogged with piles of detritus, countless totaled cars and a ubiquitous layer of mud.
Thousands have had their homes destroyed by a tsunami-like wave of muck and indignation at mismanagement of the disaster has begun.
The floods had already hit Paiporta when the regional officials issued an alert to mobile phones. It sounded two hours too late.
More anger has been fueled by the inability of officials to respond quickly to the aftermath. Most of the cleanup of the layers and layers of mud and debris that has invaded countless homes has been done by residents and thousands of volunteers.
"We have lost everything!" someone shouted.
Shouts Sunday included demands aimed at regional Valencia President Carlo Mazón, whose administration is in charge of civil protection, to step down, as well as "Where is Pedro Sánchez?"
"I understand the indignation and of course I stayed to receive it," Mazón said on X. "It was my moral and political obligation. The attitude of the king this morning was exemplary."
Spanish national broadcaster RTVE reported that the barrage aimed at the royals included a few rocks and other hard objects were tossed and that two bodyguards were treated for injuries, and the monarchs and officials called off another stop Sunday at a second hard-hit village, Chiva, about half an hour to the east of Valencia city.
Sánchez said that recovery efforts won't be derailed by the incident.
"I want to express all my government's solidarity and its acknowledgement of the anguish, suffering, uncertainty and the needs of the residents of Paiporta and the region of Valencia," Sánchez said, while adding that he believes the majority of people "reject the types of violence that unfortunately we saw today."
The mud-slinging scene occurred as thousands more Spanish soldiers, national police officers, and Civil Guard gendarmes arrived, or are set to arrive, at the disaster sites.
Wilson reported from Valencia, Spain.