For 37 years, the most extensive tornado outbreak on record, in almost every category, was the 1974 Super Outbreak, which affected a large area of the central United States and extreme southern Ontario in Canada on April 3 and April 4, 1974. Not only did this outbreak feature 148 tornadoes in only 18 hours, but an unprecedented number of them were violent; 7 were of F5 intensity and 23 were F4. During the peak of this outbreak there were 16 tornadoes on the ground at the same time. More than 300 people, possibly as many as 330, were killed by tornadoes during this outbreak. However, this record was later broken during the 2011 Super Outbreak, which resulted in 360 tornadoes and 324 tornadic fatalities. However, the most tornadoes spawned in the shortest amount of time is 104 over 5 hours and 26 minutes, during the 1981 United Kingdom tornado outbreak on 23 November 1981.