Save The Children, which supports the hospital, said four of those killed were children and two adults remain unaccounted for. The air strike came as Yemenis marked the fourth anniversary of a war which killed thousands and has starved the country.
An air strike killed seven people at a Save the Children-supported hospital on Tuesday as Yemenis rallied to show support for the Houthi movement on the fourth anniversary of a war that has killed thousands and pushed the country to the brink of starvation.
The hospital in a rural area of northwest Yemen was hit by an air strike on Tuesday killing seven people and wounding eight others, Save the Children said.
The international aid organisation, which supports the hospital, said in a statement sent to the Associated Press that four of those killed were children and two adults remain unaccounted for.
Save The Children said a missile struck a petrol station near the entrance to Kitaf rural hospital, about kilometres from the city of Saada at 0630 GMT (9:30 am local time) on Tuesday.
"The missile was said to have landed within 50 metres of the facility's main building," it said.
The organisation said the hospital had been open for half an hour and many patients and staff were arriving on a busy morning.
Among the dead were a health worker and the worker's two children and a security guard, it said.
Yemeni children at risk
Save the Children, which reported earlier this week that 37 Yemeni children a month had been killed or injured by foreign bombs in the last year, demanded an urgent investigation into the attack.
Helle Thorning-Schmidt, the organisation's chief executive, said: "We are shocked and appalled by this outrageous attack."
"Innocent children and health workers have lost their lives in what appears to been an indiscriminate attack on a hospital in a densely populated civilian area," she said. "Attacks like these are a breach of international law."
Thorning-Schmidt said the hospital is one of many Save the Children supports in Yemen, "but time after time, we see a complete disregard by all warring parties in Yemen for the basic rules of war."
The conflict in Yemen began with the 2014 takeover of the capital, Sanaa, by Iranian-backed Houthi rebels, who toppled the government of Abdrabbuh Mansour Hadi.
A Saudi-led coalition allied with Hadi's internationally recognised government has been fighting the Houthis since 2015.
Saudi-led airstrikes have hit schools, hospitals and wedding parties and killed thousands of Yemeni civilians. The Houthis have fired long-range missiles into Saudi Arabia and targeted vessels in the Red Sea.
The fighting in the Arab world's poorest country has killed thousands of civilians, left millions suffering from food and medical care shortages, and pushed the country to the brink of famine.
The United Nations is pushing ahead with tough talks with the Houthis and the Saudi-backed government to find a political solution to the conflict.
UN humanitarian chief Mark Lowcock has said about 80 percent of Yemen's population — 24 million people — need humanitarian assistance including nearly 10 million "just a step away from famine" and nearly 240,000 "facing catastrophic levels of hunger."
Thorning-Schmidt called for an immediate suspension of arms sales to the warring parties and diplomatic pressure to end the conflict.
"We must stop this war on children," she said.