Yemen has reported multiple coronavirus infections and deaths linked to the disease for the first time and an official in the southern port of Aden said the number of cases was very likely to increase in the coming days.

The United Nations has said it fears the novel coronavirus could be spreading undetected in a country where millions face famine and lack medical care after Yemen reported its first case of Covid-19 in the southern province of Hadhramout on 10 April.

Yemen has been mired in war since the Houthi group ousted the internationally recognised government from power in the capital Sanaa, prompting a Saudi-led alliance to intervene in March 2015.

The conflict has shattered health and sanitation systems and authorities lack testing capabilities.

The Saudi-backed government's health minister told Yemen TV last night that five Covid-19 cases with two deaths were reported in Aden and noted that the prevalence of other diseases with similar symptoms, such as dengue fever, made it difficult to detect coronavirus infections without testing.

"We have all been waiting for this moment and preparing for it despite our scarce (health) capabilities," said an official in the separatist Southern Transitional Council, which on Sunday declared self-rule in Aden and other southern regions.

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"Yes, this is yet another suffering for us but we must be firm, calm and patient...It is very likely the numbers will increase in coming days," Abdul Nasser al-Wali said.

The STC, which is locked in a power struggle with the Saudi-backed government in its interim seat in the south, yesterday declared a three-day, 24-hour curfew and closure of mosques.

However, the curfew was lifted after many Yemenis complained they were not ready for a lockdown.

"Thank God they retracted the decision and cancelled the curfew before we run out of food," Aden resident Khaled Morshed told Reuters.

Mosques will remain closed for two weeks, authorities said.

Authorities have told Reuters they have been unable to track down the "patient zero" responsible for Yemen's infections, an important step in tracing people potentially exposed to contagion and containing an outbreak.

Health workers say the virus could spread rapidly in ac ountry where 24 million people - 80% of the population - rely on aid, and 10 million are at risk of famine. Disease is rife.

Two sources familiar with the matter have told Reuters there has been at least one confirmed case in Houthi-controlled Sanaa, but the movement's health ministry denied this and said all suspected cases had tested negative for Covid-19.

Yesterday the Aden-based government's emergency coronavirus committee voiced concerns that Houthi officials were not admitting to a coronavirus outbreak in the capital.

The World Health Organization said it fears the worst about the Covid-19 impact in Yemen as its population has some of the lowest levels of immunity and most acute vulnerability to disease compared with other countries.

"If you look at the pattern of transmission of countries around the world we have every reason to fear that in the case of Yemen, it is being transmitted and spreading," the WHO said in a statement sent to Reuters.