NASA scientists said: "In the unlikely event that 2024 YR4 is on an impact trajectory, the impact would occur somewhere along a risk corridor which extends across the eastern Pacific Ocean, northern South America, the Atlantic Ocean, Africa, the Arabian Sea, and South Asia.".
Estimates say the rock would travel "somewhere" along a "risk corridor" above areas which are home to millions of people - but NASA data does not currently say which cities and major towns would be in this zone.
The increased odds mean the asteroid - which is around the size of a football pitch - is the most threatening to Earth in modern asteroid forecasting and would cause "severe damage" to a region if it makes impact.
Data also currently shows if the rock enters the Earth's atmosphere on 22 December 2032, it is likely to head along a large central belt of our planet and over numerous major cities.
The risk of the 2024 YR4 asteroid hitting Earth at the end of 2032 has increased again, according to NASA data.
