RNA - Flights were disrupted at the airport, in the Royal Docks area of the capital, after activists apparently in support of the Black Lives Matter movement made their way air-side, RTE reported.
"We're currently experiencing disruption to all flights due to protesters at the airport. Police are currently on the scene," An airport spokesman said.
Flights in and out of the airport were seriously affected, with no departures or arrivals were made at the airport for several hours.
It is the latest demonstration involving anti-racism activists, who brought traffic to a standstill outside Heathrow Airport, and carried out similar protests in cities around the UK, in a coordinated day of action last month.
Both British Airways and Cityjet operate flights between Dublin Airport and LCY and have seen a number of their flights cancelled or delayed over the disruption.
Passengers have been advised to check with their airline before travelling to Dublin Airport.
The Metropolitan Police are investigating how the protesters managed to get air-side.
A Scotland Yard spokesman said there were nine people on the runway who locked themselves together after erecting a tripod.
Police later tweeted that seven people had been arrested and officers were still on the scene.
In a statement, the protest group's UK division cited expansion plans at the airport as the cause of their action.
"Recently London City Airport was given approval to expand its capacity, a move that consigns the local community in Newham to further deterioration of their environment," they said.
"It is an airport designed for the wealthy. At the same time 40% of Newham's population struggle to survive on £20,000 or less. When black people in Britain are 28% more likely to be exposed to air pollution than their white counterparts, we know that environmental inequality is a racist crisis."
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