PARIS, Oct 19 (Reuters) - Europe plans to launch the first Ariane 6 rocket, its next-generation space launcher, in the fourth quarter of 2023, the European Space Agency (ESA) said on Wednesday.

The 22-nation agency had previously said it was delaying the first launch from 2022 to 2023 without giving details.

Ariane 6 is being developed by ArianeGroup, a joint venture of Airbus and Safran, on behalf of ESA in an effort to reduce launch costs in the face of new private competition from SpaceX and to secure Europe's access to space.

Developed at a cost of just under 4 billion euros ($3.9 billion) and originally set for an inaugural launch in July 2020, the project has been hit by a series of delays.

Buoyed by a major order from Amazon for its Project Kuiper constellation earlier this year, ArianeGroup subsidiary Arianespace, which operates the launches, said it had won a total of 29 orders for Ariane 6 and 7 for the smaller Vega C.

Arianespace expects some three quarters of Ariane 6 launches to come from the commercial sector, with institutional customers making up 60% of launches for the Italian-developed Vega C.

The company is looking for alternative launch slots for five missions that had been scheduled to lift off on Russian Soyuz rockets, including the Euclid space telescope and the first in a series of extreme weather warning satellites.

Arianespace Chief Executive Stephane Israel told reporters the five launches would be spread between Ariane 6, Vega C and an unspecified number of non-European launches.

Reuters reported in August that ESA had begun preliminary technical discussions with Elon Musk's SpaceX that could lead to the temporary use of its launchers after the Ukraine conflict blocked Western access to Russia's Soyuz rockets.

Industry sources have said up to two launches could be transferred to SpaceX.

The European agency plans to end operations of the three remaining Ariane 5 rockets in the first half of next year.

($1 = 1.0233 euros) (Reporting by Tim Hepher Editing by Gareth Jones and Mark Potter)