Residents of Karachi remained perplexed by 'strange' smells that pervaded large parts of the city Wednesday evening, with many taking to social media to share their concerns.

Members of the Facebook group Halaat Updates, where Karachiites discuss everything from electricity outages to municipal negligence, wondered what the reason behind the smell could be, with many voicing concerns that it may have a detrimental impact on health.

Residents of several areas in Karachi, including Gulistan-i-Johar, Gulshan-i-Iqbal, Nazimabad and parts of the Defence Housing Authority complained of the smell.

Members of the group said the smell was "unbearable" and suggested the use of face masks to cope with it.

While some describe it as the smell of rubber, others say the stench has the odour of an animal carcass.

Several people said the smell prompted their family members to search the house for a dead animal.

Some likened the smell to the stink of a dead rat, while other said it smelled like a "fish truck". One member of the group said it smelled like manure.

Other members of the group offered explanations for the causes of the smell. One member suggested the stench was a result of garbage rotting in Karachi's sweltering heat.

Another member suggested the smell was the result of a "biological attack".

Another Facebook page, Weather Updates PK, claimed that the smell was the result of an easterly shift in the wind and the strong Somalian current over the Arabian Sea.

However, it is not clear whether this forum is managed by representatives from the environmental authority.

When contacted, both Sindh Environmental Protection Agency and the the Pakistan Meteorological Department (MET) said they were not aware of the foul stench and were unable to provide an explanation.

One official, however, suggested that the odour may be due to chicken excretion dumped on the outskirts of Karachi, and that the smell could be coming due to a change in wind direction.

The official declined to be named and said he cannot give an official explanation.

"The smell has nothing to do with weather or the shifting wind," another official said.

"The smell is likely related to the environment," the official added.