Rebel shelling of government-held districts of Yemen has killed seven children over the past two days, medics and relief agencies said.

In Yemen's third largest city Taez, which is government-held but almost surrounded by rebel forces, two young girls, one just nine months old, were pronounced dead on Monday evening after a rebel bombardment that also wounded seven other people, medics said.

There was no immediate reaction from the rebels, who have repeatedly played up the high civilian death toll from air strikes by a Saudi-led coalition that has been supporting the beleaguered government.

Relief organisation Doctors without Borders appealed to "all armed groups to abide by international humanitarian law and take all necessary precautions to avoid civilian casualties".

On Sunday, five children were among eight civilians killed in rebel shelling of the government-held district of Al-Durayhimi on the Red Sea coast, medics and government source said.

The United Nations confirmed the death toll from the bombardment, which it said was part of an uptick in fighting in and around the nearby aid port of Hodeida, where a fragile UN-brokered truce has largely averted major fighting.

A total of 74 civilians were killed or wounded in Hodeida province in October as hostilities escalated, the UN mission said.

"Five children and three women were killed and another three children and three women were injured when artillery shells hit a house in Al-Ghaza village in Al-Durayhimi," said Altaf Musani, UN humanitarian coordinator for Yemen.

"This attack on women and children is unacceptable and unjustifiable."

A total of 74 civilians were killed or wounded in Hodeida province in October as hostilities escalated, the UN mission said.

The United Nations says all sides have been responsible for multiple war crimes in the conflict that has gripped Yemen since 2014, creating what UN agencies describe as the world's worst humanitarian crisis.