The United Nations said it was engaged in "intense" shuttle diplomacy between the Houthis and coalition leaders Saudi Arabia and the UAE to avert the attack.
Emirati forces with Yemeni government troops moved in from the south near Hodeida's airport, while others sought to cut off Houthi supply lines to the east, the officials said.
The assault, part of an operation dubbed Golden Victory, began with coalition air strikes and shelling by naval ships, according to Saudi-owned satellite news channels and state media.
The Security Council has strongly supported efforts by new United Nations special envoy Martin Griffiths to resume political negotiations and avoid a military escalation of the three-year-long conflict that has killed more than 10,000 people, displaced more than 2 million, and created the world's worst humanitarian crisis.
Yemen has been devastated by civil war, with the Houthi movement trying to take control of the country and forcing President Abdrabbuh Mansour Hadi to flee overseas.
Early on Wednesday, convoys of vehicles headed towards the rebel-held city as heavy gunfire rang out.
Yemen's government-controlled SABA news agency said Hadi's trip came after Emirati Foreign Minister Sheikh Abdullah bin Zayed Al Nahyan visited him at his home in Riyadh, where he lives in self-imposed exile.
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Worldwide aid agencies and the United Nations have warned the assault could shut down the vital aid route for some 70 percent of Yemen's food, as well as the bulk of humanitarian aid and fuel supplies.
The commanders spoke to an AFP correspondent in the town of Al Jah, approximately 30 kilometres (20 miles) southeast of rebel-held Hodeida. The Red Sea port is the main entry for food into a country on the brink of starvation.
Meanwhile, Col. Aziz Rashed, the spokesman for an army unit allied with the Houthis, told a news conference in the capital, Sanaa, that the rebels foiled a naval attack by government forces backed by the Saudi-led coalition in waters off Hodeida. Already, Yemeni security officials said some were fleeing the fighting. They spoke on condition of anonymity as they weren't authorized to brief journalists.
"As has been the case since the beginning of the war, the cost of the battle for Hodeida will largely accrue to the already impoverished civilian population", the International Crisis Group warned in a report Monday. A Saudi-led coalition entered the conflict in March 2015.
Yemeni forces backed by troops from the United Arab Emirates launched the assault despite UN warnings of a "catastrophic humanitarian impact".
The United Nations and other aid groups had pulled their worldwide staff from Hodeida ahead of the rumored assault.
The new United Nations envoy to Yemen, Martin Griffiths, tweeted that he was "extremely concerned" by the violence, calling on all parties to exercise restraint.