The death toll from strongest cyclone to ever hit southern Oman and neighbouring Yemen rose to 11 on Sunday, with more than 30 still missing following the torrential downpour and flooding, authorities said.

Cyclone Mekunu dumped three years' worth of rain along the Oman coast as it battered cities and seaside towns over the weekend. It downgraded to a tropical storm that struck Saudi Arabia's Empty Quarter late on Saturday with heavy rains and strong winds.

The Saudi meteorological authority on Sunday reported that winds of 60kph were kicking up blinding dust storms.

Rains are expected to continue for two more days, drenching the area with more than 100mm of rain, almost six times its annual average, Amman-based weather experts WASM said on Twitter.

Salalah, Oman’s third-largest city, received at least 278 millimetres of rainfall as the cyclone passed over. The city, which is subject to a monsoon season, typically receives 70 to 90mm of rain annually.

Omani police announced a fourth fatality from the cyclone on Sunday but gave no details. The others killed were a 12-year-old girl who was hit in the head by a door flung open by the strong winds on Friday night, an Asian labourer who died in a flooded valley and an Omani national in a SUV whose vehicle was swept away in floodwaters.

Three expatriate Asian workers remain missing, the Oman News Agency reported.

he Yemeni island of Socotra, 250km south of the mainland, is still recovering from the storm. Authorities said two died on the island, while more than 30 remain missing.

Videos of flash floods in Salalah appeared online with the first floors of homes and cars completely covered in what appears to be silt from mudslides.

Gusts reaching over 200 kilometres per hour destroyed street lights and homes along the Arabian Sea coast.

As the rain and wind subsided later onSaturday, the government mobilised the army to rescue about 300 people trapped by the flooding. A military airport in Dhofar received flown in food, medicines and clothes for the storm victims.

Omani transportation officials said the port of Salalah will remain closed but that the airport will open on Sunday, three days after it closed on Thursday.

Debris and sea foam litters a beach during Cyclone Mekunu in Salalah, Oman, May 26, 2018. Cyclone Mekunu blew into the Arabian Peninsula early Saturday, drenching arid Oman and Yemen with rain, cutting off power lines, officials said. Kamran Jebreili / AP Photo Debris litters a beach during Cyclone Mekunu in Salalah, Oman, May 26, 2018. Cyclone Mekunu blew into the Arabian Peninsula early Saturday, drenching arid Oman and Yemen with rain, cutting off power lines, officials said. Kamran Jebreili / AP Photo Debris and sea foam litters a beach during Cyclone Mekunu in Salalah, Oman, May 26, 2018. Cyclone Mekunu blew into the Arabian Peninsula early Saturday, drenching arid Oman and Yemen with rain, cutting off power lines, officials said. Kamran Jebreili / AP Photo A bird flies over the strong waves pounding a beach during Cyclone Mekunu in Salalah, Oman, May 26, 2018. Cyclone Mekunu blew into the Arabian Peninsula on Saturday, drenching arid Oman and Yemen with rain, cutting off power lines, officials said. Kamran Jebreili / AP Photo Debris litters a beach during Cyclone Mekunu in Salalah, Oman, May 26, 2018. Cyclone Mekunu blew into the Arabian Peninsula early Saturday, drenching arid Oman and Yemen with rain, cutting off power lines, officials said. Kamran Jebreili / AP Photo Strong waves and wind pound a beach during Cyclone Mekunu in Salalah, Oman, May 26, 2018. Cyclone Mekunu blew into the Arabian Peninsula early Saturday, drenching arid Oman and Yemen with rain, cutting off power lines, officials said. Kamran Jebreili / AP Photo

Sembcorp Salalah Water and Power Co, a major water desalination company and electricity plant, said it temporarily shut down its operation in Oman.

The company said its preliminary assessment suggested damage was not severe, but added that the "total impact of the cyclone on plant operations cannot yet be precisely assessed".

Residents have been warned to be wary of sudden mudslides and flash floods from within valleys in the mountainous regions. Many have evacuated to other cities along the Omani coast or farther inland.

Oman's ruler Sultan Qaboos bin Said declared a three-day holiday for government offices to allow workers to recover from the storm. Critical services such as police and civil defence workers will keep working.

Mekunu was downgraded to a tropical storm as it moved inland towards the Yemeni border and the Empty Quarter in Saudi Arabia.

The governor of Yemen's Al Marah province bordering Oman said on Twitter that the storm had destroyed homes and disrupted communication lines and water services, but no fatalities were reported.

The Yemeni island of Socotra was still recovering from the devastation caused by the storm on Saturday, with at least 30 people still missing including Yemeni, Sudanese and Indian nationals. Five Yemenis and two Indian sailors were confirmed dead, Yemen's fisheries minister Fahad Kafin said.

Rescue teams on Friday found alive four Indian sailors who were among 17 who had been reported missing on Thursday when the cyclone hit Socotra's port, and search operations are continuing for eight Indian sailors.

A plane carrying 40 tonnes of relief supplies from the Khalifa bin Zayed Al Nahyan Foundation arrived on Socotra on Saturday, state news agency Wam reported, after the Emirates Red Crescent workers reopened the main road connecting the main city of Hadibou to the airport and other areas of the island.

Mekunu was the fourth hurricane-strength cyclone to hit southern Yemen in recent years. Cyclone Sagar hit earlier this month, and in late 2015, Socotra was hit by Cyclone Chapala, followed just days later by Cyclone Megh – which destroyed hundreds of homes and killed 18 people on the island in the Gulf of Aden, about 300km from Yemen's southern coast.