The Saudi-led coalition denied any responsibility behind the air strikes on a fishing port and fish market that Yemeni medical sources said it killed 26 people in Hudaydah on Thursday, Reuters reports.
Earlier the International Committee of the Red Cross said on Twitter it was sending medical equipment to Al Thawra Hospital to treat 50 people in critical condition following the attack.
The hospital said in a tweet a strike targeted its main gate, leaving dozens of casualties while Houthi-run Saba news agency said 40 were killed in the strike.
"Coalition did not carry out any operations in Hudaydah today," the coalition spokesman, Colonel Turki al-Malki, told Alarabiya television. "The Houthi militia are behind killing of civilians in Hudaydah on Thursday," he said.
"The coalition follows a strict and transparent approach based on the international law. We pursue any allegations and if there is any responsibility we will hold it transparently," he added.
The strikes come as the United Nations tries to secure a ceasefire agreement between the warring sides.
Aid agency Save the Children said in a statement emailed to Reuters that at least one explosion went off on Thursday evening in the vicinity of Hudaydah's main hospital, where it runs a diphtheria treatment centre.
"A bomb exploded just outside the hospital, on the street. Then there was another explosion towards the back. I saw people running and bodies in the street," the statement cited a staff witness as saying.
It is unacceptable that civilians are coming under attack and that people simply walking the streets are getting caught up in this kind of violence
Saudi Arabia, the United Arab Emirates and Sunni Muslim allies have been fighting in Yemen with Western backing for more than three years against the Iran-aligned Houthis.
The Houthis control much of north Yemen including the capital Sanaa and drove its Saudi-backed government into exile in 2014.
Yemen's Houthi group said on Tuesday it was unilaterally halting attacks in the Red Sea for two weeks to support peace efforts, a few days after Saudi Arabia suspended oil exports through a strategic Red Sea channel following Houthi attacks on crude tankers on July 25.
Hudaydah port is the main conduit for supplies to Yemen, where around 8.4 million people are believed by aid workers to be on the verge of starvation.
The Saudi-led alliance says capturing Hudaydah would cut off the main supply line of the Houthis and force the group to the negotiating table, but it has made no major gains since it launched the offensive on June 12.
The Houthis have offered to hand over management of the port to the world body, according to the United Nations, but the coalition says the group must quit the western coast.