A state of emergency was declared in Karachi on Monday as stronger-than-usual monsoon rains continue to hit Pakistan's largest city, flooding homes and making streets impassable, AFP reported.

The monsoon rains, which typically last from June to September, are needed to irrigate crops and replenish lakes and dams throughout the Indian subcontinent, but they also cause destruction every year.

Pakistan is ranked eighth on the list of countries most vulnerable to extreme weather caused by climate change, according to environmental NGO Germwatch.

The Sindh provincial government declared a public holiday in Karachi and Hyderabad on Monday in an attempt to avert the chaos caused by the floods, but low-lying areas already hit hard by weeks of heavy rain have been hit hard.

The National Disaster Management Authority said at least 312 people have died since June as a result of monsoon rains.

At least two people have died in Karachi when power lines fell on flooded streets.

The heavy downpour also disrupted air and train traffic in the metropolitan area of ​​15 million people.

The worst flood in recent memory occurred in 2010, covering nearly a fifth of the country's land mass, killing nearly 2,000 people and forcing 20 million people to flee their homes.