Cyclone Shaheen had caused 11 deaths in Oman by Monday and people said towns in the northern Batinah region turned into "rivers and lakes" as hundreds of families were moved to shelters on the second day of the storm.
People living in the towns of Al Musannah, Suwaiq, Khaburah and Saham said wadis overflowed into residential areas and destroyed properties.
“I am up on my roof and can see nothing but rivers and lakes around me,” Khamis Al Hadhrami, a resident of Al Musannah, told The National.
"There is water everywhere. I can also see vehicles submerged, walls crushed, trees on the ground and waterlogged farms. It is a disaster here in Musannah."
Four deaths were announced on Sunday, including a child. Seven more died on Monday, the national emergency committee said.
Hundreds of families have been relocated to schools that have been turned into temporary shelters. On Monday, the Ministry of Education suspended classes for a week in storm-hit areas. Schools in Muscat and Al Dhahira will return on Wendesday.
By Monday, authorities said the worst of the cyclone has passed, but intermittent thunderstorms would continue. The public should remain vigilant to flash floods and stay away from Wadis, said Abdullah bin Rashid Al Khadoori, Head of the Planning and Meteorological Development Department at the Civil Aviation Authority.
Oman's Sultan Haitham on Monday ordered a ministerial committee to be formed to handle the clean-up and co-ordinate emergency efforts. He said repair of infrastructure and services like electricity and water should be expedited, state-run Oman News reported.
Salim Al Balush, a resident of Saham, said a wall in his garden collapsed.
“We heard a crashing sound and looked outside to see the compound wall collapsing,” Mr Al Balushi said.
"Then my neighbour's wall collapsed half an hour later. We called emergency services and the families in the streets, including us, were evacuated at about 11pm last night."
Farmers woke up to see their crops ruined by flooding.
"We had lettuce, tomatoes, cucumbers and melons growing very well and now everything is floating in the water," said Ahmed Al Hashmi, a farmer in Sohar.
"Our livelihoods depend on our farm. I estimate at least 2,000 rials [$5,200] of my crops are ruined."
Construction workers were also hit hard by heavy flooding.
“It was bad last night," Shakeel Rahman, a Pakistani construction worker in Suwaiq, told The National.
"We could not sleep or go out because of the heavy rain. Then this very strong wind came from nowhere and blew away our wooden hut.
"Water flooded in and swept away our beds and furniture. We walked for 20 minutes to one of the shelters while back there we lost all our possessions."
A labourer at another construction site said a fellow worker was missing after going out for a walk.
“He is just a young man in his twenties," said Akil Rahmatullah, who works in Al Musannah.
"He never came back when he went to look at the waterfalls from the mountains near by. We don’t know what happened to him."
Oman TV showed police helicopters flying people from their homes and submerged cars across the region as Ministry of Defence rescue teams searched affected areas.