Israeli officials said they expected a lengthy fight in the densely populated territory after eight days of relentless airstrikes failed to halt militant rocket attacks on Israel.
The incursion set off fierce clashes with Palestinian militants and Gaza´s Hamas rulers vowed the coastal strip would be a "graveyard" for Israelis forces.
"This will not be easy and it will not be short," Israeli Defense Minister Ehud Barak said on national television about two hours after ground troops moved in.
The night sky over Gaza was lit by the flash of bullets and balls of fire from tank shells. Sounds of explosions were heard across Gaza City, the territory´s biggest city, and high-rise buildings shook from the bigger booms.
Troops with camouflage face paint marching single file. As the ground troops moved in, Israel kept pounding Gaza with airstrikes. F-16 warplanes hit three targets within a few minutes, including a main Hamas security compound.
Witnesses in Gaza said that in the first phase, Israeli ground forces had moved several hundred yards inside Gaza. Israeli security officials said initial clashes with militants took place in open fields and soldiers did not immediately move into Gaza´s crowded cities, where warfare would likely get much deadlier.
"We have many, many targets," Israeli army spokeswoman Maj. Avital Leibovich told CNN. "To my estimation, it will be a lengthy operation."
Israel´s bruising air campaign against Gaza over the past eight days began days after a six-month truce expired. Gaza health officials say the air war has killed more than 480 Palestinians in an attempt to halt Hamas rocket attacks that were reaching farther into Israel than ever before. Four Israelis have been killed by rockets.
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