Swimming will also remain at the Olympic Aquatics Stadium but with a reduced capacity of 15,000 spectators.

Representatives from the Central and Tokyo Governments joined Tokyo 2020 and International Olympic Committee (IOC) officials at a meeting today which was fully open to the media.

It marked the partial resolution to weeks of deliberations after a Metropolitan Government Task Force suggested changes to venues in September in a bid to cut a budget which they claimed could otherwise balloon to ¥3 trillion (£22 billion/$30 billion/€26 billion).

This included a proposal to shift rowing and canoe sprint 400 kilometres away to the Naganuma rowing course in Tome in Miyagi Prefecture.

Tokyo Governor Yuriko Koike praised these plans at the beginning of today's meeting and emphasised that the Naganuma course would have reflected the Olympic aim to use existing venues.

But she then conceded that the initial proposal was stronger due to its better location and the likely need for expensive overlay costs at Naganuma.

The IOC than announced that Naganuma will instead be used as a training facility ahead of the Games.

No final costing for the Sea Forest venue was confirmed, but Koike urged the International Rowing Federation and International Canoe Federation to shoulder some of the burden as well as the Japanese authorities.

The Metropolitan Government report in September suggested that it may cost ¥49.1 billion (£349 million/$436 million/€411 million).

It is hoped, however, that the final figure will be considerably lower.

Koike also outlined how reducing the swimming capacity from 20,000 to 15,000 seats would be a necessary way to reduce costs at the aquatics venue rather than consider an alternative location.

The Governor, who was elected to her post in July, then asked for extra time to consider a potential move of the volleyball venue to Yokohama.

Current plans are for a new Ariake Stadium to be constructed within the city.

She claimed to want to carry out a full architectural review of both venues to assess the accuracy of cost projections.

Her ideas were questioned by Tokyo 2020 President Yoshirō Mori, however, who queried whether Yokohama even wanted to host the event.

In a backwards and forwards exchange which raised the tension-levels in the room, Mori also appeared to suggest that the Metropolitan Government's alternative venue plans had "dropped from heaven" rather than arising from a detailed survey.

Koike replied that Yokohama authorities had assured her that, if they are chosen, they would like to play host.

Japanese Olympic Committee President Tsunekazu Takeda also defended the Ariake Arena plan.

It would provide one of the "only legacies for international competitions" from the Games, he said, adding that it would also be able to host the winter sports of ice hockey and figure skating.

Koike's proposal was accepted by the IOC, although its Coordination Commission head John Coates did describe the Christmas deadline as "ambitious".

"It will take immense hard work and real goodwill from all partners to meet a Christmas deadline," added the IOC executive director for the Olympic Games, Christophe Dubi.

"I think it is ambitious, but, if we set this deadline, let's roll up our sleeves and continue to work as hard as we have over the last few months."

As well as Koike, Mori and Coates, others present today included Japanese Olympics Minister Tamayo Marukawa.