... The catalyst for the chain of events in the spring of 1989 was the death of Hu [Yaobang] in mid-April; Hu was transformed into a martyr for the cause of political liberalization. On the day of his funeral (April 22), tens of thousands of students gathered in Tiananmen Square demanding democratic and other reforms. For the next several weeks, students in crowds of varying sizes—eventually joined by a wide variety of individuals seeking political, social, and economic reforms—gathered in the square. The initial government response was to issue stern warnings but take no action against the mounting crowds in the square. Similar demonstrations rose up in a number of other Chinese cities, notably Shanghai, Nanjing, Xi’an, Changsha, and Chengdu. However, the principal outside media coverage was in Beijing, in part because a large number of Western journalists had gathered there to report on the visit to China by Soviet leader Mikhail Gorbachev in mid-May. Shortly after his arrival, a demonstration in Tiananmen Square drew some one million participants and was widely broadcast overseas.
(source: Britannica - The Online Encyclopedia)