World Population Day is observed annually on 11 July to raise awareness of global population issues. The date was chosen because it was on or around 11 July 1987 that the world's population reached five billion people. That figure is now nearly 7.5 billion, and the United Nations estimates it will be around 11.2 billion by the year 2100. Part of the problem is that people are living longer – life expectancy at birth increased from 30 to 67 between 1800 and 2005.
China is the world's most populous country with around 1.4 billion inhabitants, but its population is falling, and India is catching up rapidly.
This year's theme is "investing in teenage girls" who face a lack of school and early marriage and motherhood which leaves them vulnerable to illness, injury and exploitation.
The growth of the world's population affects sustainability, urbanisation, health, inequality, poverty and global warming. To mark World Population Day 2016,
IBTimes UK presents this gallery of overcrowding and huge gatherings around the globe. People crowd onto a bridge that they believe can help them escape tribulations and illnesses during the annual Caiqiaohui event in Mianyang, Sichuan province, China Reuters An artificial wave pool is packed by would be swimmers to escape the summer heat in Daying county in Sichuan province, China China Daily/Reuters People scramble to reach the roof of an overcrowded train at a station in Dhaka, during the annual festival of Eid al-Adha in 2015 Roberto Schmidt/AFP Scooters and motorcycles at a junction during rush hour in Taipei, Taiwan, in 2009 Nicky Loh/Reuters People try to touch the religious icon of the Black Nazarene during the annual procession in the Philippines capital Manila on 9 January 2015 attended by over 5 million people Ted Aljibe/AFP Devotees try to form a human pyramid during celebrations to mark the Hindu festival of Janmashtami in Mumbai, India Danish Siddiqui/Reuters Students practice tai chi on a playground at a high school in Jiaozuo, Henan province, China, during a Guinness World Record attempt for the largest martial arts display, on 18 October 2015 Reuters A traffic jam near a toll station on a huge highway as people return home at the end of a week-long national day holiday, in Beijing, China, on 6 October 2015 China Daily/Reuters Commuters disembark from crowded suburban trains during the morning rush hour at Churchgate railway station in Mumbai, India Vivek Prakash/Reuters Jobseekers visit booths of companies at a job fair for graduates in Nanjing, Jiangsu province, China Sean Yong/Reuters Applicants walk into the entrance of a university to take part in the entrance exam for postgraduate studies in Wuhan, Hubei province, China Reuters Shi'ite Muslims gather at the shrine of Imam Hussein during Ashura commemorations in Karbala, Iraq, on 4 November 2014 when an estimated 20 million people visited the holy site Mohammed Sawaf/AFP Muslim pilgrims pray at the Grand Mosque in the holy city of Mecca during the annual hajj pilgrimage File photo Ibraheem Abu Mustafa/Reuters Lifeguards attempt to control the crowd as people visit the beach on new year's day in Durban, South Africa, on 1 January 2014 Rogan Ward/Reuters A crowded beach in Durres, on the Albanian Adriatic AFP Couples pose for a group photograph during a mass wedding ceremony at the Taipei Flora Expo Hall in Taiwan on 9 September 2010 Nicky Loh/Reuters Commuters are held outside Oxford Circus tube station in London, United Kingdom, to regulate numbers Matthew Lloyd/Getty Images Buses and commuters cross the diagonal crossing, aimed at easing crowding, at Oxford Circus in London, United Kingdom Stefan Wermuth/Reuters Commuters wait for a train at a subway station in Sao Paulo, Brazil Nacho Doce/Reuters Passengers crowd into a departure hall while waiting to board trains at a railway station in Wuhan, in China's Hubei province, during the annual new year mass migration Reuters People walk along a crowed shopping street on the first day of the winter sales in Barcelona, Spain David Ramos/Getty Images Staff push a passenger into a crowded subway train at the Ikebukuro station on the Marunouchi line during rush hour in Tokyo, the Japanese capital Kim Kyung Hoon/Reuters A passenger uses a window to board a crowded train at a railway station in Hefei, Anhui province, during China's new year travel peak season Jianan Yu/Reuters Laundry hangs outside a student dormitory at a college in Wuhan, Hubei province, China Reuters Residential buildings in Po Lam, one of Hong Kong's satellite towns. About 25 percent of the world's tallest 100 residential buildings, over 200 metres tall, are in the territory Bobby Yip/Reuters Thousands of internally displaced people queue for the distribution of goods at Kibati camp near the city of Goma in the eastern Democratic Republic of Congo on 10 December 2008 Peter Andrews/Reuters An overcrowded train leaves a platform in Tongi near Bangladesh's capital Dhaka in 2003, as pilgrims flock to the annual Ijtema Muslim gathering Rafiquar Rahman/Reuters High rise residential buildings are seen behind a slum in Mumbai, India, on 20 July 2010 Danish Siddiqui/Reuters The fairground lights up during sunset on the opening day of Oktoberfest in Munich in September 2014. An estimated six million people attend the 16-day festival Joerg Koch/Getty Images Hindu pilgrims make their way over pontoon bridges near Sangam during the Maha Kumbh Mela in Allahabad, India Daniel Berehulak/Getty Images