Tropical Cyclone Shaheen hit land in Oman on Sunday having already killed at least three people.
Its heavy rain and ferocious winds prompted evacuations from coastal areas and delayed flights to and from the capital, Muscat.
When its eye crossed land, the cyclone was carrying winds of between 120 and 150 km per hour (75-93 mph), Omani authorities said. It was throwing up waves of up to 10 metres (32 feet).
Video footage from local broadcasters showed vehicles submerged as people tried to make their way through muddy brown floodwater.
As the storm approached, a child who had been swept away by water was found dead, the state news agency said, and another person was missing.
Two Asian workers were killed when a hill collapsed on their housing area in an industrial zone, the state news agency reported.
Part of the eyewall of the storm, where the most severe weather occurs, had entered Al Batinah South governorate, the state news agency said.
The eye also entered between the states of Musanah and Suwaiq.
Massive rainfall of as much as 500 cm (20 inches) was expected in some areas, potentially causing flash floods.
Cyclone epicenter makes landfall between Al Musanaa and A’Suwaiq, accompanied by heavy rains and strong winds whose outskirts swing ranges between 120 km and 150 km https://t.co/EmQkErVVnU— وكالة الأنباء العمانية (@OmanNewsAgency) October 3, 2021