I wonder if Saigon/HCMC shouldn't be considered as the correct answer for Vietnam. The city maps I'm finding seem to extend the city limits to the sea.
It's one of these tricky examples that depends on which definition of a "coastal city" you chose.
The definition I decided to take (indicated in the first caveat) is to look at the urban areas. While the administrative limits of Ho Chi Minh City does reach the sea, its urban area doesn't when you look from the sky so I decided not to count it as a valid answer
The poulation is by urban area. If you look on the map, Guayaquil and Yangon are separated from the ocean, as they lie on rivers. São Paulo itself is located on a plateau and doesn't come near the ocean. The one which surprise me was Kuala Lumpur but it turns out it is connected to the ocean via Port Klang.
By looking from the sky Fao doesn't seem to be connected to Basrah by its urban area so I'll still consider Basrah as an invalid answer (even if I totally admit that it makes the Iraqi answer pretty difficult haha)
I took Wikipedia as a source when citypopulation.de was not enough, Machala is indicated to have a 246 000 inhabitants metro population and 226 000 for Manta.
Always hard to know if the source information is perfect for inhabitants statistics but I'll keep following this
The definition I decided to take (indicated in the first caveat) is to look at the urban areas. While the administrative limits of Ho Chi Minh City does reach the sea, its urban area doesn't when you look from the sky so I decided not to count it as a valid answer
Always hard to know if the source information is perfect for inhabitants statistics but I'll keep following this