1964 Calcutta riots
The 1964 Calcutta riot was a religious riot that occurred in January 1964 and spread throughout the city of Calcutta. The violence primarily targeted Muslims and was perpetrated by members of the Hindu community. This event was the first intense religious violence in the city since the 1946 riots. The violence included attacks resulting in bloodshed, property destruction, and organized looting, which led to the death of at least 264 people, according to official records. Unofficial estimates of casualties ranged from 100 to 500. The aftermath of the riot left the Muslim community in Calcutta feeling more segregated and fearful than ever before. Reports indicated that as many as 70,000 Muslim residents fled their homes. Background
The violence in Calcutta began to develop on December 27, 1963, when a sacred relic believed by many to be a strand from the beard of Islamic Prophet Muhammad was stolen from the Hazratbal Shrine in Jammu and Kashmir. This incident sparked protests and mass agitation, which fueled hatred towards the minority Hindu community in East Pakistan (present-day Bangladesh) and eventually led to a violent riot in the border districts of present-day Khulna Division, resulting in the deaths of 29 Hindus. Despite strict international border controls, several hundred Hindu refugees crossed into the adjacent Hindu-majority Indian state of West Bengal due to the harsh conditions of the riot. As they moved towards Calcutta, approximately 30 miles from the frontier, they spread stories and rumors of atrocities in Khulna and Jessore, which incited retaliation against Muslims in rural areas of West Bengal. By the evening of January 9, 1964, the impoverished slums on the eastern outskirts of Calcutta began to stir. Timeline

8th January 
The news of violence against Hindus in East Pakistan spread throughout the city and suburbs by local press and migrated refugees. The resentment of the Hindu community first started to appear at the late hours of 8th January as Muslim stalls in the Sealdah area of central Calcutta were shut down by Hindu mobs. 9th January 
Public meetings were held in various parts of the city to protest against the aggression of Muslims towards Hindus in East Pakistan. A large procession marched to the Deputy High Commissioner of East Pakistan demanding protection from the Pakistani government for Hindu victims and ensuring proper punishment for the people involved in violence there. They also burned effigies of Pakistani President Ayub Khan. The problems precipitated when an evening procession mostly done by students was attacked by a Muslim group with sticks, bricks, and soda-water bottles at Wellington Crossing. The same night a Hindu was stabbed to death by Muslim mobs in central Kolkata resulting in intense hatred among local Hindus which developed central Kolkata into the hotspot of the riot in the coming days. 10th January 
On the morning of Friday, January 10, communal incidents occurred in the Taltolla, Beniapukur, Entally, and Beliaghata police station areas of Calcutta where stray cases of assault, arson, and looting were reported. The police opened fire on five occasions and used 36 rounds of tear gas. Besides this, Hindu students in and around Calcutta boycotted schools and colleges and organized a march to Pakistan High Commissioner in order to protest against the communal violence in East Pakistan, which took the life of 29 Hindus. During this, a sudden involvement and confrontation of police caused the death of a protester named Bahudeb Sen, a BA first-year student from Andrew’s College, who was shot by police firing near Jadavpur. The situation began to get worse after that and evoked considerable agitated response among the youth, the masses, and the intelligentsia. On the other hand, the Bangaon region along with Maheshtala, Rajabazar, Beliaghata, Entally and Sonarpur witnessed mob clashing with the police. 11th January 
The riot started to reach its peak intensity in Calcutta as the Army had to be called in on 11th January to quell the rioting. The areas of Jadavpur, Budge-Budge, Metiabruz, Maheshtala and Sonarpur were clamped with 10pm-5am curfew. The situation at the outskirts of the city was also grim as in Gaighata near Bangaon three policemen were killed by a group of Hindu mobs because the policemen ordered the Hindus not to attack a Muslim village. Units of the Indian Army moved into Calcutta in the afternoon to reinforce the city. The army opened fire on mobs and looters twice before nightfall, according to official reports. 8 of the city's 10 police wards were silenced by a dusk‐to‐dawn curfew that night, and soldiers patrolled the streets in the slum areas in eastern Calcutta. By night, the officials estimated that over sixty people were killed in the last three days. More than 50 cases of arson were reported just on that one day. 12th January 
The riot continued with the same intensity on 12th January. Mosques and Muslim shops and homes were set afire with kerosene‐soaked rags. Harsh violence were continued to be reported from various parts of the city like Sealdah, Taltola, Beliaghata, Entally, Beniapukur, Garia. The death toll was not announced that night, although nine more dead bodies were to yet to be found. Another army battalion was ordered to Calcutta along with three police battalions from neighboring states to establish law and order in the city. 13th January 
The condition of the Muslim community became very harsh by 13th January. The official death toll crossed 100, more than 70,000 Muslims were estimated  to fled their homes in the city, and 55,000 were sleeping in the open under army protection at that point of time. Although there had been several incidents of stabbing and bombing, most of the riots resulted in the looting and burning of Muslim property. More than 110 people had to be hospitalised following the shootings and firemen had to deal with 200 cases of arson since the start of the riot. Two rubber factories were set on fire along with a number of shops and dwellings. A 24-hour curfew was extended to five areas of the city occupied by police officers following the increase in number of arson attacks and looting against Muslims. Buses and trams were taken off the road and most shops and markets had been shut down. The Indian Government claimed the trouble in Calcutta to be a 'huge loss of life'. References

1964 in India
Crime in Kolkata
History of West Bengal (1947–present)
Riots and civil disorder in India
Anti-Muslim violence in India
Religiously motivated violence in India