The World Health Organization has confirmed that the first cases of polio seen in China since 1999 were caused by a strain that spread from Pakistan.
The polio strain WPV1 that was identified in China has been genetically linked to a type that is currently circulating throughout Pakistan, according to the BBC.
Nine cases have been confirmed in the Chinese province of Xinjiang, which lies against the eastern border of Pakistan, Reuters reports.
The WHO also warned that the virus, which can cause paralysis, has the potential to spread even further afield during the Muslim pilgrimage period known as the Haj.
Polio, which affects the nervous system, can cause severe paralysis and is considered highly infectious. The disease is generally spread through contaminated food, drinking water and feces.
In Xinjiang province, several polio cases have been detected in the last two months. Chinese authorities are investigating the outbreak and have launched a massive inoculation campaign in the surrounding area.
"So far all the right things are being done," WHO spokesman Oliver Rosenbauer said, Reuters reports.
The WHO warned that polio is considered to have spread nationwide in Pakistan, mainly because of a disruption in vaccination efforts caused by recent insecurity, particularly in the Khyber tribal region.