Six Spanish tourists were raped by a gang of armed, masked men in the Mexican resort of Acapulco, the latest chapter of violence that has tarnished the once-glamorous Pacific coast resort.

The vicious, hours-long attack occurred before dawn Monday at a house that six Spanish men, six Spanish women and a Mexican woman had rented on a quiet, idyllic stretch of beach on the outskirts of Acapulco.

The attackers gained access to the house because two of the Spaniards were in the yard and apparently were forced to open the door, said Acapulco Mayor Luis Walton at a news conference late Monday.

The five attackers burst into the house and held the group at gunpoint, he said. They tied up the six men with phone cords and bathing suit straps and then raped the six Spanish women. The Mexican woman was not raped.

The attack began about two hours after midnight Monday and the victims were only able to report the crime five hours later, at nearly seven in the morning.

"This is a regrettable situation, and of course it is going to damage Acapulco," Walton said.

Attackers wore masks

The once-glittering resort that attracted movie stars and celebrities in the 1950s and 60s has already been battered by years of drug gang killings and extortions, but except for very few incidents, the violence has not touched tourists.

Walton said he believed, but wasn't sure, that the assailants in Monday's attack didn't belong to a drug gang. Guerrero state Attorney General Martha Garzon Guzman said witness descriptions of the attackers were more difficult to obtain because they wore masks.

"From what the attorney general has told me, I don't think this was organized crime," Walton said. "But that will have to be investigated, we don't know."

Mexico's Foreign Relations Department issued a statement saying it regretted the attack, and suggesting it was not drug-cartel related.

"Up to now, the investigations are being carried out by local authorities and they will be the ones to provide information," the statement said.

In Mexico, federal authorities investigate drug-related crimes.

Security and drug analyst Jorge Chabat said that, after years of drug gang activity in Acapulco, the distinction may be merely semantic.

"At this point, the line between common and organized crime is very tenuous, there are a lot of these gangs that take advantage of the unsafe situation that currently exists, they know the government can't keep up," Chabat said. "Everything points to this being organized crime, because several gangs have operated there for years ... it's probably not the big cartels, but there are smaller groups that carry out crimes on a permanent basis."

The Spanish Embassy in Mexico City said the victims were receiving consular assistance.

The victims were "psychologically affected" by the attack and received treatment, the mayor said.

Travellers advisory

Spain's Foreign Ministry had already issued a travellers advisory on its website for Acapulco before the Monday attack, listing the resort as one of Mexico's "risk zone," though not the worst.

"In Acapulco, organized crime gangs have carried out violence, though up to now that has not affected tourists or the areas they visit," the advisory states. "At any rate, heightened caution is advised."

A travel advisory from Canada's Foreign Affairs department tells Canadians to "exercise extreme caution" in the state of Guerrero, including Acapulco, "due to high levels of organized crime and urban violence."

The attack came just three days after a pair of Mexican tourists returning from a beach east of Acapulco were shot at and slightly wounded by members of a masked rural self-defence squad that has set up roadblocks in areas north of Acapulco, to defend their communities against drug gang violence.

The vigilantes say the Mexican tourists failed to stop at their improvised roadblock.

Walton said the city was already contemplating ways to revive the city's image.

"We have to look at an advertising campaign to say that not everything in Acapulco is like that," Walton said. "This happens everywhere in the world, not just in Acapulco or in Mexico."

The attack was particularly embarrassing for Mexico, because it came just four days after Tourism Secretary Claudia Ruiz Massieu visited the International Tourism Fair held in Madrid to launch a "promotional offensive" depicting Mexico as a safe and attractive destination.

"This is Mexico's moment," Massieu said, describing it as "a safe country."