"We are preparing for a strong hit," Cuban Vice President Carlos Lage told state television.
Cuba's National Meteorological Institute said heavy rains were soaking the entire eastern half of the island of 11 million, and dangerous storm surges were threatening communities along most of the northeastern coast.
Ike's powerful winds sent huge chunks of debris flying over the streets of the central-eastern city of Camaguey, which was just 20 miles (35 kilometers) north of the eye at 8 a.m. (1200 GMT).
Diagonal sheets of stinging rain flooded the narrow colonial streets, which were further clogged with tree branches, metal grates and plastic sheeting.
A huge sheet of plastic roofing spun like a top in the wind above a traffic intersection. Streets were deserted, save for a lone, miserable-looking security guard taking shelter at a bus station.
State television earlier broadcast images of the storm surge washing over coastal homes in the easternmost city of Baracoa. It said huge waves surged over buildings as tall as five stories and dozens of dwellings were damaged beyond repair.
A tally of sporadic reports from six of the eight eastern provinces affected indicated at least 900,000 people had evacuated, and former President Fidel Castro released a statement calling on Cubans to heed security measures to ensure no one dies. Cuba historically has successfully carried off massive evacuations before hurricanes, sparing countless lives.
Ike had weakened to a Category 2 storm with top sustained winds near 100 mph (155 kph) and forecasters expected further weakening as it moved over central Cuba on Monday. It was moving west near 14 mph (22 kph).
Winds reaching as high as 160 mph (260 kph) damaged an undetermined number of homes in Holguin province. Roofs were ripped away and trees toppled across the region.
Foreign tourists were pulled out from vulnerable beach communities, including more than 9,000 from the resort of Varadero, east of Havana. Workers rushed to protect coffee plants and other crops, and plans were under way to distribute food and cooking oil to disaster areas.
Forecasters said Ike would likely hit Havana, the capital of 2 million people, early Tuesday. Morning skies were only cloudy, but schools were closed and domestic flights were suspended Monday.
On Florida's Key West, tourists and residents alike were ordered to evacuate and a steady stream of traffic filled the highway from the island. Ike was forecast to make landfall later in the week between the Florida Panhandle and the Texas coast - with New Orleans once again in the cross hairs.
The hurricane also slowed efforts to bring oil and gas production back online in the Gulf of Mexico following Hurricane Gustav.
In Camaguey, municipal workers boarded up banks and restaurants before heavy rain started falling. More than 100 people waited in chaotic bread lines at each of the numerous government bakeries around town as families hoarded supplies before the storm.
"There's no fear here, but one has to be prepared. It could hit us pretty hard," said Ramon Olivera, gassing up his motorcycle.
On the provincial capital's outskirts, trucks and dented school buses brought about 1,000 evacuees to the sprawling campus of an art school. Classrooms at the three-story school built on stilts were filled with metal bunk beds.
Mirtha Perez, a 65-year-old retiree, said hardly anyone was left in her nearby town of Salome.
"It's a huge evacuation," she said. "We are waiting and asking God to protect us and that nothing happens to us."
Strong gusts and steady rains fell at the U.S. naval base at Guantanamo Bay in southeast Cuba, where all ferries were secured and beaches were off limits. The military said cells containing the detainees - about 255 men suspected of links to the Taliban and al-Qaida - are hurricane-proof. But the base was spared the strongest winds.
Ike first slammed into the Turks and Caicos and the southernmost Bahamas islands as a Category 4 hurricane, but thousands rode out the storm in shelters and there was no immediate word of deaths on the low-lying islands.
In flooded Haiti, Ike made an already grim situation abysmal.
At least 58 people died as Ike's winds and rain swept the impoverished Caribbean nation Sunday. Officials also found three more bodies from a previous storm, raising Haiti's death toll from four tropical storms in less than a month to 319. A Dominican man was crushed by a falling tree.
Haiti's coastal town of Cabaret was particularly hard hit - 21 victims were stacked in a mud-caked pile in a funeral home there, including two pregnant women, one with a dead girl still in her arms.
Off Mexico, Tropical Storm Lowell was moving northwest parallel to the coast with maximum sustained winds of 60 mph (96 kph). The hurricane center predicted it will veer into the Baja California Peninsula late in the week.
Associated Press writers Ben Fox in Providenciales, Turks and Caicos; Mike Melia in Nassau, Bahamas; Jonathan Katz in Gonaives, Haiti; Alexandra Olson in Cabaret, Haiti; Anita Snow in Havana, Cuba; and Danica Coto and David McFadden in San Juan, Puerto Rico, contributed to this report.