Tens of thousands of Yemenis have been fleeing Hodeidah as fighting intensifies on front lines near the Houthi-held western province, Amnesty International said on Thursday, warning that "the worst is yet to come" if the war reaches urban areas.

Forces backed by a Saudi-led military coalition are advancing toward Hodeidah port city, long a key target in the three-year war, though local officials told Reuters this week they do not plan to launch an assault on densely populated areas nearby.

The United Nations puts the number of displaced along Yemen's western coast in recent months at some 100,000 people, most of them from Hodeidah, the second most populated province, the rights group said.