The strongest tropical storm to hit the Gulf for decades has lashed Oman.
Cyclone Gonu struck the capital Muscat, snapping tree branches, damaging buildings, and leaving roads flooded.
Meanwhile, residents along the coast of southern Iran are preparing for the storm, moving to higher ground and sheltering in schools and mosques.
The Iranian town of Jask has reported high winds, heavy rain and overflowing rivers. The main road north is reported to be impassable because of flooding.
In Muscat, roads were flooded and visibility was almost zero at times. Residents experienced cuts in mains electricity and water supply.
BBC user Siva Reddy said the downpour started early in the morning after a period of intense heat.
"Strong winds started battering the trees and the TV dish antennas fixed on top of the buildings started flying around like missiles," she said.
Police had warned people in Muscat to stay indoors and the streets were largely deserted. Some 20,000 people have been evacuated in the oil-rich sultanate.
Omani ports were closed and flights suspended at Muscat airport, but shipping in the Strait of Hormuz, which carries up to 40% of world oil supplies, has not been disrupted.
The authorities at Sohar port closed all operations and evacuated the 11,000 workers.
"These people know the force of the sea and they're doing the right thing," said port spokesman Dirk Jan De Vink. "Most of them are leaving or have already left."
If shipping is halted in the strait, analysts said there could be panic in world oil markets and a steep rise in prices, at least for a short period.
In the last 24 hours Cyclone Gonu has diminished in force, two days after peaking at a maximum Category Five designation over the Arabian Sea.
The cyclone initially generated winds of 160mph (260km/h), but latest reports say they have now dropped to 50-70mph.
In south-west Pakistan, fishing boats were told to stay ashore until the storm passed.
A cyclone is the meteorological name for hurricanes in the Indian Ocean and western Pacific.
Are you in Oman or southern Iran? Do tell us what's happening and send us any pictures you have of the cyclone.
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115pm Muscat Central Time. I am currently viewing the typhoon brushing the coasts from Azaiba beach, it has been raining solidly since 2am last night. Sources inform me that Amerat, Qurm & Al Khuwair have been affected by severe flooding & blown away trees. Many residents are cut off by flooded roads and some are facing electricity brownouts.
S Al Lamki, Muscat, Oman
It's absolutely tipping down here. The windows in our house are leaking like mad. We're running round with mops but it just won't stop. Outside our garden is flooding!! 2 of our trees have fallen down almost hitting our neighbour's car. Tomorrow when the wadis fill up its going to be chaos. School has been cancelled today but by the end of the weekend I think we'll be really bored. From Amy, 12 years old.
Amy McGuigan, Muscat
Its 1300 hrs Local time (+4 hrs GMT) here in Muscat, the capital city of Oman. Heavy rains with winds are lashing the city and the main roads are deserted. There is sufficient daylight equivalent to that of twilight but many low lying areas are inundated.
Anand, Muscat, Oman
I have lived in Oman for nearly 10 years and I have never experienced something like this. The schools are closed, we have been told the water and power is going to be cut. We have also been told to fill buckets and bathtubs with water and to stock up on food supplies for at least 5 days! The houses in Oman are not strong enough to withstand the winds and the rain is pouring down inside our homes. Even though we know we are going to be safe, there will be a lot of damage done and it is not safe outside the house.
Andre Waerness-Vold, Muscat, Oman
I live in the Madinat Qaboos area that is near where last March's devastating drench flooded the Qurum area and flooded the entire area whilst putting an instant halt to business for two whole days. It is said that we would feel the force of it by 2am Oman Main Time. I am hoping that this cyclone will just blow by the coastal area and never hit Muscat. It doesn't seem we really are prepared and the disaster would be outstanding.
Ali Mehdi, Muscat, Sultanate of Oman
I live and work in Oman for the past 12 years and I love this beautiful country. This is one of the most clean and organised countries in the world. However, we are all informed about the forthcoming threat of Gonu cyclone. His Majesty the Ruler of this country has kindly declared holidays from today till Saturday 9 June. There is high security arrangement and the people from the coastal area have been evacuated to safer destination and these people are well cared for.
Mary Vasaikar, Muscat, Oman
All offices and public institutions have closed down in anticipation of the cyclone. I doubt anything but the general food stores and coffee shops will be open tomorrow. It's actually 19:10 Tuesday evening and there is the most incredible sunset I have ever seen in Oman, everything is quite calm and there are lots of clouds which is unusual for this time of year.
Daniel , Nizwa, Oman
Clouds have been over coastal mountains since this morning - no rain yet - winds constant at about 15-20 mph - feels like a storm is coming... but not yet.
Michael Benz, Muscat, Oman
I am living in Qurm which is the main commercial area of Muscat. Weather conditions are stable. There skies are very cloudy with a little bit of wind. The sea is closer than it usually is to the shore. Other than that all is good where weather is concerned.
Mohammed Al Moosa, Qurm ,Oman
The Omani government has declared holidays from today until Sunday. Till 19:00 hrs the thing are normal on weather front but a strange kind calmness is witness here.
Sagar Kulkarni, Muscat, Oman
Nothing much, as yet. Very heavy cloud cover, but no rain in central Muscat (18.48 local time). Storm predicted to hit Muscat between 12 midnight and 2 a.m. local time. All business and schools closed at 2 p.m. today and many people headed to petrol stations and supermarkets who quickly reported selling out of fuel, food and water. We are 50 metres from beach and although sea is choppy, there is no other sign of an impending storm.
Jane, Muscat, Oman
We had cyclone in 1981 and 300 peoples died in Oman, but we expect this one to be much bigger than the one we had in 1981, but this time the government is well ahead prepared for the outcome, let us hope we will overcome the tragedy. Jamal Y. Jaffer - Muscat
Jamal Yousuf Jaffer, Wadi Kabir, Muscat - Oman
It has been a very hectic day here in Muscat. In the afternoon the queues in the supermarkets were up to 3 hours long. Everything has been closed down now. If you have not been able to get groceries by now, then forget it. People are staying inside. The waves in Muttrah which is the port of Muscat have started to reach over the barriers and onto the roads. The authorities are keeping regular updates on the television.
Kristin Norman Berg, Muscat, Oman
We have lived here for a few years now and have seen some pretty serious storms. However, people seem to be panicking about this one, and I can only assume it is because we are actually getting warnings about it. There is little to no adequate drainage here and that always compounds any issue with rain fall. People are always getting flooded out in Muscat, but people are always ready to help each other here... no matter their nationality or religion.
Alison Hardy, Muscat, Sultanate of Oman