The first wave was expected to hit the Big Island by 11:19 a.m. local time, 4:19 p.m. ET, but that time has passed without unusually large wave activity measured along Hawaii's shores.
Hawaii Gov. Linda Lingle had said waves as high as 7½ feet could strike the Hilo area on the Big Island but much smaller 1½-foot waves are expected in Honolulu Harbor on Oahu.
Civil defense sirens blared in each county of Hawaii starting at 6 a.m. Hawaiian time as residents and tourists calmly began leaving their coastline homes and resorts and moving to higher ground. It was the first widespread evacuation for a tsunami in 16 years.
"The most important thing you could do is heed the instructions of state and local officials," President Obama, a Hawaii native, advised citizens in a statement today outside the White House.
"There is a tsunami in the water, in the Pacific, headed our way," said Nathan Becker with the Pacific Tsunami Warning Center.
Becker warned Hawaiians that the waves could be "going on for hours through the afternoon."
Red Cross officials are urging people to gather food and supplies to remain self-sufficient for at least three days.
Grocery stores faced a crush of residents eager to stock up on food, water and batteries. Long lines of cars snaked through many islands' streets near gas stations as drivers filled their tanks.
"We've got a lot of things going for us," Charles McCreery, director of the center, told The Associated Press. "We have a reasonable lead time. The evacuation should all take place during daylight hours, and wave impact should be during daylight hours."
Jayson Lum Kalani, a resident of Oahu, told ABCNews.com he was awakened by the sounds of the sirens blaring early in the morning.
"I thought it was a work crew," he said, noting that the sirens usually sound off the first day of each month as part of an emergency test system.
Kalani said he was not nervous about the pending tsunami on Oahu but had heard from friends on the Big Island who had evacuated. "It depends on what side of the island you are on [on the Big Island]," he said. "Hilo is more in the [tsunami's] path."
As a precautionary measure, the U.S. Navy has ordered four ships to leave the port of Pearl Harbor and remain at sea, where they will escape the crush of incoming water that could thrust them against the shore.
"This is a serious event," said Hawaiian Sen. Daniel Inouye. "If you live in the evacuation zone, I urge you to gather your family and please leave the area."
The PTWC warning advises "urgent action should be taken to protect lives and property."
An estimated 40,000 to 50,000 people are in the affected areas of the Big Island and are said to be evacuating.
Emergency workers have begun going door to door urging people to heed the sirens, and homeless people who live on the beaches are being transported away in buses.
Buck Giles, a dispatcher with the Ocean Safety and Lifeguard Services Division for the City and County of Honolulu, told ABC News about 500 homeless people who live on the beach on the west side of Oahu are being taken from higher ground.