Over a dozen people are dead and hundreds have been sickened by a gas leak in the southern port city of Karachi, according to Pakistan health officials, the Associated Press reports. 

According to a senior health official, the death toll reached 14 as of Tuesday. 

The leak that began on Sunday set off a panic in the city as officials were unable to identify the source and the type of gas that was involved. Scientists and chemical experts from the army and navy have been deployed to areas to try to find the source of the leak.

The odorless gas, which causes severe breathing problems, led many residents rushing to local hospitals. So far, more than 650 people have been treated, mostly from the Kamari neighborhood. 

Residents rallied on Tuesday, demanding the source of the leak be traced quickly. Meantime, Syed Murad Ali Shah, chief minister in Sindh province, said that authorities were still unable to determine the cause of the gas leak.