Hong Kong, Sep 20 (IANS): Authorities in Hong Kong were Friday bracing themselves against a super typhoon that intensified overnight and is predicted to make landfall just kilometres from the city, media reported Friday.

Hong Kong's observatory issued a warning that super typhoon Usagi intensified Thursday night into a super typhoon and "poses a threat to Hong Kong" Sunday, South China Morning Post reported.

The observatory's storm tracker showed the typhoon to be on a direct trajectory toward the city.

"By that time the weather will deteriorate significantly, with high winds and rough seas," the observatory said.

"If you are planning to travel out of Hong Kong or (have) other activities (scheduled), please be reminded that changes in the weather may affect your plans."

An expert from the School of Energy and Environment at the City University of Hong Kong said the power of Usagi could be on par with Typhoon Megi in 2010 and also some of the major ones that hit Hong Kong in the 1980s.

He said that often typhoons reaching the southern Chinese coast are weakened by first hitting Taiwan or the Philippines.

But as Usagi would pass between Taiwan and Philippines, "it won't have a chance to weaken before it reached the southern coast of China", said typhoon expert Johnny Chan Chung-leung.

Chinese authorities Friday issued a disaster relief alert ahead of the typhoon which they said was expected to hit the coastal regions of southern China's Guangdong province Sunday.

Cheng Yuen-chung, senior scientific officer of the Hong Kong Observatory, said Usagi could become the strongest typhoon of the year to hit Hong Kong, especially if it wasn't weakened by a land mass before reaching the city.