The opening of a second international airport for Mexico City has resulted in safety incidents including warnings that aircraft were in danger of flying into the ground, a pilot association said.

Air traffic controllers appear to have received little training and support on how to operate the new configuration, the International Federation of Air Line Pilots' Associations (IFALPA) said in a safety bulletin dated May 4.

The organization said it had "been made aware of several incidents involving aircraft" at Mexico City International Airport, since Felipe Angeles International Airport opened north of the capital on March 21.

They included planes arriving "with low fuel states due to unplanned holding, diversions for excessive delays, and significant GPWS (ground proximity warning system) alerts," it said.

"One crew almost had a controlled flight into terrain," it added.

The International Air Transport Association defines such an incident as "an in-flight collision with terrain, water, or obstacle without indication of loss of control."

IFALPA urged crews to consider carrying additional fuel in case they have to wait for permission to land or divert to another airport, and to exercise heightened terrain situational awareness.

Experts have previously highlighted the challenges of operating two airports in a city surrounded by mountains and at an altitude of more than 2,200 meters (around 7,300 feet) above sea level.

So far airlines are operating only a small number of daily flights from Felipe Angeles International Airport, a flagship project of President Andres Manuel Lopez Obrador built at a military air base north of the capital.

The existing Mexico City International Airport, also known as Benito Juarez, is one of the busiest airports in Latin America.

It handled a record 50.3 million passengers in 2019 before the Covid-19 pandemic.

Lopez Obrador announced this week a plan to reduce arrivals and departures at Benito Juarez and transfer more operations to Felipe Angeles.