LONDON, England (AFP) — London 2012 organisers said they were investigating why there were so many empty seats at Olympic venues yesterday, the first day proper of the Games.

Organisers LOCOG were overwhelmed with demand for Olympics tickets when they first went on sale more than a year ago.

But some venues had large areas of empty seats Saturday, notably the Aquatics Centre and at the Wimbledon tennis complex, causing sports fans to vent their fury outside venues and on social media.

"We are aware that some venues have empty seats," a LOCOG spokesman told AFP.

"We believe the empty seats are in accredited seating areas, and we are in the process of finding out who should have been in the seats and why they weren't there."

Normally a match between a British hopeful and a former world number one on the 15,000-seater Centre Court at Wimbledon would be played before a packed house.

But the bowl was half-empty as British number two Anne Keothavong took on Denmark's Caroline Wozniacki.

"Very surprised at amount of empty seats on Wimbledon Centre Court, especially as I applied for some! It can't be more than 50 percent full," wrote Alex Dover on Twitter.

Britain's Olympics minister Jeremy Hunt called the situation "very disappointing".

"We're looking at this very urgently," he told BBC television.

If sponsors are not going to turn up and take their seats, "we want those tickets to be available for members of the public", he said.

There were also significant numbers of empty seats at the Aquatics Centre, despite a much-anticipated showdown between America's Michael Phelps and Ryan Lochte.