ISLAMABAD, Pakistan — The authorities are trying to determine the cause of 14 deaths in the southern port city of Karachi, with officials giving conflicting explanations.

Hundreds have fallen sick from the apparent poisoning, which has left people with chest pains, breathing difficulties and burning eyes.

Some officials have attributed the illnesses and deaths to a gas leak that started Sunday evening in Keamari, a coastal neighborhood close to Karachi’s main port. Word of the apparent leak quickly spread panic in several other neighborhoods, and nervous residents and traders staged a protest on Tuesday against the authorities over their failure to detect the cause of the problem.

At least 500 people have reported being sickened, with many hospitalized in critical condition.

Schools and factories have been closed in Keamari, and Pakistan State Oil has temporarily suspended operations at an oil terminal at the port.