Yemeni pro-government forces advanced closer to rebel-held Hodeida overnight, a military source said on Wednesday, raising fears over humanitarian aid deliveries through the lifeline port city.
Concern was also growing for civilians in Hodeida, as the fighting drew near and after reports that snipers had positioned themselves on a hospital rooftop.
Plumes of smoke were seen billowing from the horizon on Tuesday as heavily armed pro-government forces moved towards the Red Sea port on foot and on the back of pickup trucks.
A pro-government military source said on Wednesday that loyalists backed by a Saudi-led coalition made "limited advances" overnight towards Hodeida and its port, through which more than 70 per cent of the impoverished country's imports pass.
The coalition, an alliance led by Saudi Arabia and the United Arab Emirates, had sent fighter jets and Apache attack helicopters to cover Yemeni troops fighting rebels on the ground, the source told AFP.
A barrage of 100 air strikes were fired at the weekend around Hodeida, the Save the Children aid group said, citing its staff in the city of 600,000 residents.
In the past 24 hours fighting claimed the lives of 27 rebels and 12 pro-government fighters on the outskirts of Hodeida city, a medical source told AFP on Wednesday.
Nearly 200 combatants have been killed in the past week, according to military sources.
Hospitals in crossfire
The United Nations children's fund, UNICEF, on Wednesday voiced concern an escalation in the violence would jeopardise humanitarian efforts crucial for the survival of millions across the war-torn country.
"The concern really is that if Hodeida port doesn't function anymore, we, as UNICEF, are then not able to bring in humanitarian supplies through that port," Juliette Touma, spokeswoman for the UN agency, told AFP.
Touma said that in past years UNICEF had been able to transport to Hodeida humanitarian supplies using "little boats".
This week marks one year since the government coalition, which controls Yemen's airspace and maritime borders, imposed a blockade on rebel-held Hodeida in retaliation for Huthi missile attacks on Saudi Arabia.
Rights groups now fear for civilians, as fighting nears two hospitals in the area.
A medical source told AFP on Wednesday that the Huthis had forced medical staff out of the May 22 Hospital -- one of Hodeida's main medical facilities -- and stationed snipers on top of the building.
UNICEF warned on Tuesday the fighting was dangerously close to Al-Thawra hospital in southern Hodeida, and was endangering the lives of 59 children.
The clashes come as the United Nations pushes to restart negotiations between the warring parties, after planned talks in Geneva in September failed.
The International Committee of the Red Cross on Wednesday appealed for warring parties to "spare civilians and civilian infrastructure" including ambulances, hospitals, electricity and water plants.
"Families are staying in schools -- each classroom housing two or three families -- which makes it an average of 20 people in the classroom with nothing whatsoever," said Mirella Hodeib, ICRC spokesman in Sanaa.
"ICRC urges all parties to respect international humanitarian law... and to allow for the safe passage of civilians who want to flee the active conflict zones."
Hodeida, one of the last Huthi strongholds on Yemen's western coast, was seized by the rebels along with the capital Sanaa in 2014.
Saudi Arabia and its allies intervened in the government's fight against the Huthis months later, driving the rebels from a string of ports but failing to retake the capital and Hodeida.
Hodeida is Yemen's most valuable port, crucial for aid delivery and food imports to a country where famine looms over 14 million people and a child dies every 10 minutes from easily preventable diseases, according to the UN.
Saudi Arabia and its allies accuse Iran of using Hodeida port to smuggle missiles to the Huthis, a charge Tehran denies.
The World Health Organization estimates nearly 10,000 people have been killed in Yemen's war since 2015, although rights groups say the toll could be five times higher.