(Bloomberg) -- A growing number of flights were delayed at major airports in the New York City area as smoke from fires across eastern Canada blanketed the region, casting an eerie yellow glow in the sky and reducing visibility for pilots.

Ground delays were in place at LaGuardia Airport and Newark Liberty International Airport Wednesday afternoon, as well as at Philadelphia International Airport, according to the Federal Aviation Administration’s website. A brief ground stop for flights headed to LaGuardia was lifted at 1:57 p.m.

“The FAA has slowed traffic to and from the New York City area airports due to reduced visibility from wildfire smoke,” the agency said in a statement. It “will adjust the volume of traffic to account for the rapidly changing conditions.”

Health officials urged New York City residents to stay indoors on Wednesday as unhealthy air quality levels posed a risk to the sick, elderly and young children. 

Delta Air Lines Inc. is experiencing delays but doesn’t expect any cancellations at LaGuardia, a spokesman said. It has the largest share of passengers there, at 21%. The airline provides protective gear for employees who request it and break rooms for those who work on the airport tarmac.

United Airlines Holdings Inc., which accounts for 56% of Newark’s passengers, is “adjusting our schedule where needed” and monitoring the situation and employees who work outside, a spokesman said.

About 29% of flights, or 165, headed to LaGuardia were delayed while 22%, or 125, departing flights were late, according to data from FlightAware. About 6% of operations were delayed at John F. Kennedy International Airport, while 17% of inbound Newark flights were delayed and 8% of outbound.

The FAA actions due to the smoke were the same as they routinely take for thunderstorms, fog and other weather events. When visibility falls, air-traffic controllers typically add distance between planes to minimize the risks of a midair collision, and that will slow the number of arrivals an airport can handle.

An FAA advisory said that planes arriving at LaGuardia can expect to have to hold before landing until midnight local time. Delays were expected to run about 119 minutes per flight, the agency said.

(Updates throughout with details)

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