Sonear posted the asteroid was the "largest that has passed closest to Earth this year".
Three other asteroids also raced past Earth on Thursday, but none of them were as close or as large as 2019 OK, the report said.
"An asteroid on a trajectory to impact Earth could not be shot down in the last few minutes or even hours before impact".
Astronomers refer to these asteroids as "city killers".
Basically, experts reckon the asteroid would hit with 30 times the power of the Hiroshima atomic bomb.
Astronomers had no idea the rock was heading towards our planet, due to the asteroid flying towards us from the direction of the sun.
Nasa's planetary defense officer, Lindley Johnson, says scientists have found 95 percent of all near-Earth objects measuring one kilometer (two-thirds of a mile) or bigger.More news: Google wants your face data in return for a $5 gift card
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Associate Professor Michael Brown, from Monash University, said: "It's impressively close". According to a statement offered by a well-known astronomer, the impact between Earth and the asteroid could have led to severe damage.
In a separate comment to the Herald, Dr Brown said: "This is one of the closest approaches to Earth by an asteroid that we know of". An elliptical orbit didn't allow the asteroid to spend a lot of time near Earth and it traveled at about 54,000 miles per hour, a higher than average speed.
The space rock zoomed past Earth at a very close distance, at least for space, coming within 45,000 miles of our planet.
2019 OK has a very elliptical orbit, taking it from the asteroid belt beyond Mars to within the orbits of both Earth and Venus.
For example, back in 2013, a meteor snuck up on us and exploded over the Russian city of Chelyabinsk; that blast was stronger than a nuclear explosion, and the resulting shock wave shattered glass down below and injured more than 1,000 people.
Asteroid 2015 HM10, which is up to 360 feet wide, also flew by Earth. "We actually have the technology to find and deflect certainly these smaller asteroids if we commit to now".
It passed by at a distance of 356,000km on Wednesday.
The Earth just experienced the equivalent of strolling down the street and minding your own business when suddenly a baseball whistles by your ear. Brown said Asteroid 2019 OK proves there are "still unsafe asteroids out there that we don't know of" that "can arrive on our doorstep unannounced".