Flood waters forced tourists in hotels and shelters to climb to higher floors, as Wilma ripped away shop fronts and peeled back roofs.
On the Mexican island of Cozumel, a navy rescue mission sighted three bodies floating down a flooding avenue and a fourth in a town square.
Wilma had weakened to a Category 2 hurricane with winds of 160kph as it crawled northward, but was expected to pick up speed and strength on Sunday, sideswiping Cuba before it slams into Florida.
The hurricane's centre was located 85km north of Cancun late on Saturday night.
After a lull, violent winds and rains hit Cancun again after dark on Saturday, pushing flood waters even higher.
The hurricane sent water surging over the narrow strip of sand housing the city's luxury hotels and raucous bars, joining the sea with the resort's crocodile-infested lagoon on Saturday.
Lobbies were gutted as waves from the open sea slammed into some low-lying hotels, Quintana Roo state Governor Felix Gonzalez announced.
Cancun residents had ventured briefly from their hiding spots to survey the flooded, debris-filled streets as the eye of the storm passed the famous resort.
Winds return to Cancun
But Wilma's winds returned and continued to make reconnaissance by state and federal authorities almost impossible.
Several dozen people looted at least four convenience stores, carrying out bags of canned food while others dragged tables, chairs and lamps from a destroyed furniture shop.
Roaring waves pounded Mexican
beach resorts on Thursday
Police were guarding only larger stores, including a downtown Wal-Mart and an appliance store.
Downtown Cancun was littered with glass, tree trunks and cars up to their roofs in water.
The front half of a food outlet had collapsed, and at least one petrol station had its roof blown away.
Yucatan Governor Patricio Patron told Formato 21 radio that one person was killed by a falling tree, but he offered no details. And in Playa del Carmen, two people died from injuries they sustained on Friday when a gas tank exploded during the storm, Quintana Roo state officials said.
The storm earlier killed 13 people in Jamaica and Haiti.
Quintana Roo State Civil Protection Director Major Jose Nemecio said a few emergency crews were able to begin distributing emergency supplies in Playa del Carmen, to the south of Cancun, where screaming winds had flattened wood-and-tarpaper houses.
On Cozumel, which has been isolated since weathering the brunt of the storm on Friday, the navy announced on Saturday it had evacuated a family of seven from a partially collapsed house and moved several stranded residents and a tourist to shelters.
But further rescue operations were suspended because of severe weather.
In Cancun, the wind ripped part of the ceiling off a gymnasium-turned-shelter, forcing the evacuation of more than 1000 people late on Friday. Stacy Presley, a 22-year-old honeymooner from Milwaukee, was among them.
She and 120 others were moved to a kindergarten where evacuees were forced to use plastic water bottles instead of toilets and sleep on miniature desks nearly submerged in rising flood waters. There was no food available to them.
"There were people getting sick from the urine on the floor. We had to do something, so we took off. We were running through flooded streets, passing downed power lines"
22-year-old honeymooner from Milwaukee in Cancun
She and her husband fled when the winds died down. "There were people getting sick from the urine on the floor," she said.
"We had to do something, so we took off. We were running through flooded streets, passing downed power lines." She ended up at another school sheltering more than 2000 people. It had mats to sleep on, emergency officials and supplies.
Nearby, Loni Steingraph, 40, of Austin, Texas, praised the shelter, saying: "I booked a four-star hotel, I didn't know it would include a four-star shelter too."
Benjamin Rodriguez, 49, of Cleveland, spent the night in a classroom with his 11-month-old granddaughter. He and several others had to lean against a door that the wind kept shoving open.
"I feel for the citizens here because we get to go home eventually," said Rodriguez, who came with 32 family members for his son's wedding. "They have to stay and rebuild everything that was destroyed."
Well inland, Juan Carlos Fernandez, a 39-year-old clothing designer, said the winds were so strong that he and two friends shuttered themselves in a closet.
Everything went flying
"Everything went flying. The electric garage door went flying," he said. "I'm afraid - very, very afraid.
President Vicente Fox planned to travel to the affected region on Sunday.
The army and navy prepared to move in emergency supplies, including food, water, medicine and roofing. Fox said they would be sent in as soon as possible.
The US embassy was sending consular officials to shelters on Sunday, an effort to help people prepare for the evacuation of about 30,000 tourists after the storm.
Wilma smashed aircraft in Playa
del Carmen in Quintana Roo
The US government also offered to donate $200,000 in hurricane aid.
In Cuba, the government evacuated more than 500,000 people, while a tornado spun off from the storm flattened 20 homes and several tobacco-curing huts.
The twister demolished the wooden home of Caridad Garcia, who huddled with her family in the bathroom, the only room left standing. "It sounded like the world was coming to an end," said Garcia, 58.
Record 22nd storm
Sunday could bring an additional 25cm to 40cm of rain to the already saturated Yucatan peninsula and western Cuba, according to the US National Hurricane Centre in Miami.
Officials posted a hurricane watch for the entire southern Florida peninsula, the Florida Keys, Florida Bay and the Dry Tortugas ahead of Wilma.
At the same time, a record 22nd tropical storm of the Atlantic hurricane season formed off the island of Hispanola, shared by Haiti and the Dominican Republic, where authorities warned of possible deadly flash floods and mudslides.
Officials used the Greek alphabet to name Tropical Storm Alpha, after running all the way through the 2005 storm name list.