"The recent escalation in armed clashes in Hodeidah could result in up to 1.1 million people requiring emergency food assistance," the agency said on Twitter.
WFP teams have been working around the clock since the announcement of the offensive to procure and preposition food stocks and ready-to-eat food packages in the besieged area.
The Saudi-led coalition of mostly Gulf Arab states said it hoped to end an impasse in the four-year war with Houthi rebels controlling the port, but humanitarian agencies fear the assault could cut off the lifeline for Yemenis, most of whom rely on outside help for survival.
On Wednesday, Saudi-led forces launched a full-scale offensive to recapture al Hodeidah from Houthi rebels. As the city is the main entry point for humanitarian aid, some organizations voiced concern over the escalation of the situation.