Firemen and paramedics are seen outside the Helmut Schmidt airport in Hamburg, Germany February 12, 2017. The airport was closed after unknown substance was found during security check. [Photo/Agencies]

HAMBURG - German authorities said on Sunday the leak of a corrosive substance through the air conditioning system at Hamburg airport was not an attack, adding that police were investigating the incident that forced the brief closure of the facility.

Firefighters and ambulances were rushed to the scene after some 50 people at one terminal complained of eye irritation and breathing difficulties.

"I want to explicitly deny ... that this was a terrorist attack. As far as we know it was at no period considered a terrorist attack," Hamburg fire department spokesman Torsten Wessely told a news conference in the northern city.

"A pepper spray-like canister has been found during our investigative searches which might be the source," he added.

He said the substance was spread through the facility's central air conditioning system.

Lightly dressed passengers were rushed outside the terminal in almost freezing temperatures, leaving their coats and jackets behind in the hurry. They were allowed back in shortly after.

A spokeswoman for the airport said flights had resumed as of 1.45 p.m. (1245 GMT).

According to live flight tracking website flightradar24.com some flights were diverted to other airports after the incident.