The Storm Prediction Center said the highest number of confirmed tornadoes recorded in April since 1950 was 267 in 1974, Accuweather.com reported Tuesday.
Forecasters noted the 600 for April 2011 are reports or sightings, not confirmed tornadoes.
Many times multiple sighting of single tornadoes are recorded, and it will be a while before the data can be analyzed and the number of confirmed tornadoes determined, Accuweather said.
May and June are normally the most active months for severe weather, but meteorologists say an unusually active April does not necessarily mean high levels of tornadoes will continue.
"When you see ... an April that is very busy, you don't typically see May and June also to be very active, because the pattern that really supports the very active tornadic activity in April doesn't necessarily continue it, as the threat moves farther to the north and to the east," AccuWeather.com's Senior Meteorologist Ken Reeves said.
In most years that had a busy April for tornadoes, May and June were not particularly active, Reeves said.