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Ethnicity

The oldest portions of modern Karachi reflect the ethnic composition of the first settlement, with Balochis and Sindhis continuing to make up a large portion of the Lyari neighbourhood, though many of the residents are relatively recent migrants. Following Partition, large numbers of Hindus left Pakistan for the newly independent Dominion of India (later the Republic of India), while a larger percentage of Muslim migrant and refugees from India settled in Karachi. The city grew 150% during the ten year period between 1941 and 1951 with the new arrivals from India, who made up 57% of Karachi's population in 1951. The city is now considered a melting pot of Pakistan and is the country's most diverse city.

Karachi is the largest Bengali speaking city outside Bengal region.

In 2011, an estimated 2.5 million foreign migrants lived in the city, mostly from Afghanistan, Bangladesh, Myanmar, and Sri Lanka.

Much of Karachi's citizenry descend from Urdu-speaking migrants and refugees from North India who became known by the Arabic term for "Migrant": Muhajir. The first Muhajirs of Karachi arrived in 1946 in the aftermath of the Great Calcutta Killings and subsequent 1946 Bihar riots. The city's wealthy Hindus opposed the resettlement of refugees near their homes, and so many refugees were accommodated in the older and more congested parts of Karachi. The city witnessed a large influx of Muhajirs following Partition, who were drawn to the port city and newly designated federal capital for its white-collar job opportunities. Muhajirs continued to migrate to Pakistan throughout the 1950s and early 1960s, with Karachi remaining the primary destination of Indian Muslim migrants throughout those decades. The Muhajir Urdu-speaking community in the 2017 census forms slightly less than 45% of the city's population. Muhajirs form the bulk of Karachi's middle class.

Karachi is home to a wide array of non-Urdu speaking Muslim peoples from what is now the Republic of India. The city has a sizable community of Gujarati, Marathi, Konkani -speaking refugees. Karachi is also home to a several-thousand member strong community of Malabari Muslims from Kerala in South India. These ethno-linguistic groups are being assimilated in the Urdu-speaking community.

During the period of rapid economic growth in the 1960s, large numbers Pashtuns from the NWFP migrated to Karachi with Afghan Pashtun refugees settling in Karachi during the 80's. Karachi is home to the world's largest urban Pashtun population, with more Pashtun citizens than the Peshawar. Pashtuns from Afghanistan are regarded as the most conservative community. Pashtuns from Pakistan's Swat Valley, in contrast, are generally seen as more liberal in social outlook. The Pashtun community forms the bulk of manual labourers and transporters. Anatol Lieven of Georgetown University in Qatar wrote that due to Pashtuns settling the city, "Karachi (not Kabul, Kandahar or Peshawar) is the largest Pashtun city in the world."

Migrants from Punjab began settling in Karachi in large numbers in the 1960s, and now make up an estimated 14% of Karachi's population. The community forms the bulk of the city's police force. The bulk of Karachi's Christian community, which makes up 2.5% of the city's population, is Punjabi.

Despite being the capital of Sindh province, only 6–8% of the city is Sindhi. Sindhis form much of the municipal and provincial bureaucracy. 4% of Karachi's population speaks Balochi as its mother tongue, though most Baloch speakers are of Sheedi heritage – a community that traces its roots to Africa.

Following the Indo-Pakistani War of 1971 and independence of Bangladesh, thousands of Urdu-speaking Biharis arrived in the city, preferring to remain Pakistani rather than live in the newly independent country. Large numbers of Bengalis also migrated from Bangladesh to Karachi during periods of economic growth in the 1980s and 1990s. Karachi is now home to an estimated 2.5 to 3 million ethnic Bengalis living in Pakistan. Rohingya refugees from Myanmar, who speak a dialect of Bengali and are sometimes regarded as Bengalis, also live in the city. Karachi is home to an estimated 400,000 Rohingya residents. Large scale Rohingya migration to Karachi made Karachi one of the largest population centres of Rohingyas in the world outside of Myanmar.

Central Asian migrants from Uzbekistan and Kyrgyzstan have also settled in the city. Domestic workers from the Philippines are employed in Karachi's posh locales, while many of the city's teachers hail from Sri Lanka. Many Sri Lankans moved to Karachi due to the 2022 Economic Crisis in Sri Lanka. Expatriates from China began migrating to Karachi in the 1940s, to work as dentists, chefs and shoemakers, while many of their descendants continue to live in Pakistan. Chinese also reached Karachi after 2015 in large number due to the CPEC project. The city is also home to a small number of British and American expatriates.

During World War II, about 3,000 Polish refugees from the Soviet Union, with some Polish families who chose to remain in the city after Partition. Post-Partition Karachi also once had a sizable refugee community from post-revolutionary Iran.