An armed conflict was triggered after December 21, 1963, a period remembered by Turkish Cypriots as Bloody Christmas, when a Greek Cypriot policemen that had been called to help deal with a taxi driver refusing officers already on the scene access to check the identification documents of his customers, took out his gun upon arrival and shot and killed the taxi driver and his partner.
In the morning after the shooting, crowds gathered in protest in Northern Nicosia, likely encouraged by the TMT, without incident. On the evening of the 22nd, gunfire broke out, communication lines to the Turkish neighborhoods were cut, and the Greek Cypriot police occupied the nearby airport.
On the 23rd, a ceasefire was negotiated, but did not hold. Fighting, including automatic weapons fire, between Greek and Turkish Cypriots and militias increased in Nicosia and Larnaca. A force of Greek Cypriot irregulars led by Nikos Sampson entered the Nicosia suburb of Omorphita and engaged in heavy firing on armed, as well as by some accounts unarmed, Turkish Cypriots. The Omorphita clash has been described by Turkish Cypriots as a massacre, while this view has generally not been acknowledged by Greek Cypriots.
Further ceasefires were arranged between the two sides, but also failed. By Christmas Eve, the 24th, Britain, Greece, and Turkey had joined talks, with all sides calling for a truce.
On Christmas day, Turkish fighter jets overflew Nicosia in a show of support. Finally it was agreed to allow a force of 2,700 British soldiers to help enforce a ceasefire. In the next days, a "buffer zone" was created in Nicosia, and a British officer marked a line on a map with green ink, separating the two sides of the city, which was the beginning of the "Green Line". Fighting continued across the island for the next several weeks.