More than a million people have fled their homes as the Texas-size storm bore down on the coast.
Gargantuan waves smashed over the city's seawall as the center of Ike was about 85 kilometers (55 miles) southeast of Galveston, moving at near 20 kilometers (13 miles) an hour, the Miami-based National Hurricane Center reported.
At 0300 GMT Saturday, the hurricane was packing winds of 175 kilometers (110 miles) an hour, just shy of becoming a powerful Category Three storm on the five-level Saffir-Simpson scale, the center said.
Ike was expected to plow ashore early Saturday, with a direct hit on Galveston and Houston.
In Galveston, the power went out across the island just before 0100 GMT Saturday, plunging the storm-stricken city into darkness.
Galveston Mayor Lyda Ann Thomas ordered a dusk-to-dawn curfew starting Friday and ending Monday morning.
Chocolate-colored seawater flooded the streets as the storm surge intensified throughout the day, spoiling the city's potable water