Polio has broken out in China for the first time since 1999 after being imported from Pakistan, and there is a high risk of the crippling virus spreading further during the Haj pilgrimage, the World Health Organization said.

Nine cases have been confirmed in China so far, six children and three adults, all in Hotan prefecture in the western province of Xinjiang, WHO spokesman Oliver Rosenbauer said. All are genetically linked to the polio virus circulating in Pakistan, the United Nations agency said.

Polio is now considered to have spread nationwide in Pakistan, mainly due to insecurity that has halted vaccination campaigns in areas including the Khyber tribal region, he said.

China had been considered polio-free since the last known case imported from India in 1999, Rosenbauer said.

Chinese authorities are investigating whether the latest cases are related to each other and have launched a vaccination campaign targeting millions of children, he said. 'So far all the right things are being done,' he told Reuters.

The outbreak marks the latest setback to a global campaign to eradicate polio, now endemic in only four countries -- Afghanistan, India, Pakistan and Nigeria. In 1988, when the  drive began, the virus paralysed nearly 1,000 children each day.

Pakistan has reported 84 polio cases so far this year, up from 48 at the same time last year, according to the WHO.

Most cases are in three zones -- the Federally Administered Tribal Areas (FATA) including Khyber, Balochistan province particularly greater Quetta, and Sindh province, especially Karachi. But tests on water in sewage systems outside these areas had also detected the virus transmitted by human excrement, indicating 'nationwide transmission', it said.

'The WHO rates as 'high' the risk of further international spread of wild polio virus from Pakistan, particularly given the expected large-scale population movements associated with Umra and the upcoming Haj,' it said in a statement.

The Haj, which is due to start in November, attracts millions of pilgrims to Makkah each year.

The WHO recommended that all travellers to and from Pakistan have full protection with three or more doses of oral polio vaccine. Saudi authorities already require all travellers to have been vaccinated within six weeks before entering the kingdom, with a further dose upon their arrival, it said.

Sanofi Aventis' unit Sanofi Pasteur said in a separate statement that it was donating a polio vaccine strain to the WHO for use in its eradication campaign.

'With this donation from Sanofi Pasteur, WHO will be in full control of the storage of the vaccine strain and its distribution to vaccine producers worldwide,' Sanofi said.

The viral seed is used to produce oral polio vaccines against type 3 polio virus. Polio is caused by three strains of polio virus, and while type 2 has already been eliminated, it is hoped types 1 and 3 will be wiped out within a few years.

'We now have all three seed strains we need to produce oral polio vaccine. It helps us manage the global vaccine supply,' WHO's Rosenbauer said.  - Reuters