Three policemen have been killed during a shootout with two other officers suspected of drug trafficking at Mexico City's airport, as panicked travellers scrambled for cover in the busy facility.

The incident occurred on Monday when three federal officers approached the two suspects at Benito Juarez's Terminal Two, which handles international and domestic flights.

Two agents were killed at the terminal and another later died of his injuries in hospital.

More than a dozen shots were heard, local Milenio Television reported.

Television footage showed a body lying on the floor of the terminal in what appeared to be a publicly accessible area of the airport.

The suspects, who remain at large, are believed to be part of a larger group of officials involved in a cocaine ring, the security ministry said in a statement.

Airport spokesman Jorge Gomez told Milenio that aircraft departures and arrivals continued normally after the incident.

Mexico City has seen relatively low murder rates compared to the rest of the country, where drug violence has killed about 55,000 people in the past five and half years.

But attacks have been creeping up in the capital and its surrounding neighbourhoods, with more than 300 gangland killings recorded last year.

Mexico's airports and ports are busy areas for drug smugglers. So far this year federal police have seized more than 200kg of cocaine at the capital's airport, double the amount taken there last year.