Updated

Mexican authorities scrambled Wednesday to clear landslides blocking the only roads out of Acapulco while tourists lined up to be airlifted out as the rain-drenched country braced for new storms.

At least 57 people have died in Mexico since major storms hit opposite coasts this week, the first double onslaught in 50 years, unleashing floods and mudslides that still affect much of the country.

New threats emerged as the US National Hurricane Center warned that a tropical cyclone could form on the east coast while Manuel, which had dissipated after making landfall on Sunday, regenerated into a tropical storm south of Baja California.

Further south on the Pacific coast, workers toiled to remove a mountain of mud stuffed in a tunnel and rocks strewn on the two roads linking Acapulco to Mexico City.

The state of Guerrero, where Acapulco lies, has been the hardest hit by the deluge, registering 27 deaths while 15,000 people have been placed in shelters.

President Enrique Pena Nieto warned that the roads would remain shut until at least Friday or Saturday.

"One of our major priorities is opening traffic between Acapulco and Mexico City," Pena Nieto told reporters after visiting the former haunt of Hollywood stars.

He said opening the roads is urgent "not only for people who have to travel on that road and have to go home, but also because it is obviously an important supply route."

With the airport submerged in dark water, the military and commercial carriers set up an airlift that has flown around 3,000 rain-weary holidaymakers to Mexico City since Tuesday.

The military has brought 60 tonnes of supplies and 8,000 liters of water to Acapulco, Defense Secretary Salvador Cienfuegos said.

Helicopters will deliver food in mountain ares and look for people who need to be evacuated.

In Acapulco, more than 40,000 Mexican and foreign beachgoers have been marooned in the flooded city for five days, with more than half of Acapulco covered by floods.

Amid the chaos, thousands of people looted a Costco wholesale store on Tuesday, wading out of the flooded shop with televisions, food and even fridges.

"Unfortunately, there is desperation, but more army and navy troops have arrived," Mayor Luis Walton told MVS radio. "We ask people to remain calm."

Some 2,000 tourists have taken shelter in a concert hall, where airlines set up makeshift check-in counters, while 1,000 more were housed in a convention center.

"It was a hellish vacation," said Cynthia Aguilar, a 26-year-old Mexico City resident waiting in line to get on a flight.

While Acapulco is no longer a favorite haunt of Hollywood stars, and drug gang violence has risen, several tourists were keeping the nightlife alive amid the floods, drinking and eating in bars playing loud music.

"We endured a horrible weekend without light, water or food. The water began to rise as much as one meter (three feet)," said Maria Fernanda Gonzalez, 27, drinking a beer with friends at a beachfront bar.

On the city's main boulevard, cars were abandoned in front a gas station that had run out of gas.