Residents in Lanzhou, capital of Northwest China's Gansu province, snapped up bottled water on Friday after the city's tap water was found to be polluted by benzene, a toxic cancer-causing chemical, China News Service reported.

The public's panic buying came after Veolia Water, the major drinking water supplier, detected high levels of benzene in its water sample — one that was 11 to 20 times the limit of 10 micrograms per liter of water — between Thursday night and Friday morning.

The city's Xigu district cut off the water supply, and Lanzhou's environmental protection department said an investigation is underway.