The risk of a sizeable asteroid hitting the Earth is significantly growing every few years, Czech scientists who analysed 144 fireballs from a recent meteor shower had warned.An asteroid strike on Earth is just a matter of time and it could destroy major cities, experts have said.Researchers from the Astronomical Institute of the Czech Academy of Sciences recently showed that a "new branch" of Taurids contains at least two asteroids of the size 200-300 metres.The warning comes ahead of the Asteroid Day to be observed on June 30. Shower Curtain Manufacturers According to Alan Fitzsimmons from Queens University Belfast in Britain, it is a case of when an asteroid collision will happen, rather than if it will happen."Over 1,800 potentially hazardous objects have been discovered so far, but there are many more waiting to be found," he said. Researchers found that this was due to a well-defined orbital structure.. On that day in 1908, a small asteroid exploded over Tunguska in Russias Siberia, levelling trees and burning the ground over 2,000 square kilometres. Experts including Apollo 9 astronaut Rusty Schweickart and International Space Station astronaut Nicole Stott will answer questions from people on social media.This year, discussions and presentations will be streamed live from Luxembourg on June 30. But it is still possible the next Tunguska would take us by surprise, and although we are much better at finding larger asteroids, that does us no good if we are not prepared to do something about them," he added.The Taurid meteor shower showed significantly enhanced activity in 2015.Mr Fitzsimmons said an unexpected strike today by an asteroid similar in size to the one that exploded over Siberia could easily destroy a major city, and a larger asteroid could be more dangerous."Astronomers find near-Earth asteroids every day and most are harmless."It is important to know that scientists and engineers have made great strides in detecting near-Earth asteroids and understanding the threat posed by them," Mr Fitzsimmons said.