WASHINGTON (AFP) - Hundreds of thousands of people tuned in to a flight tracking website on Tuesday (Aug 2) anxious to find out whether US official Nancy Pelosi was in fact going to Taiwan, in defiance of China's angry protests.

Trouble was, there were so many of them - a site record of over 708,000 - that Flightradar24 said it had to limit non-subscribers' access in order to keep the service online.

"Unfortunately, due to the volume of users, it was necessary to deploy our waiting room functionality, which meters access," the company said in a statement, referring to "unprecedented" interest.

The sudden fixation on the plane carrying Pelosi, dubbed SPAR19, was driven in large part by uncertainty over whether the US House Speaker would go through with the trip she had refused to confirm.

It's significant because Pelosi, second in line to the presidency, is the highest-profile elected US official to visit Taiwan in 25 years and Beijing has made clear that it regards her presence as a major provocation.

Once the plane landed safely on the Taipei tarmac - speculation had grown that China might take action against the jet - the mystery was no more and the curious crowd dispersed.

"Shortly after SPAR19 landed, normal access for all users was restored quickly," Flightradar24 said.

China considers self-ruled, democratic Taiwan as its territory and has vowed to one day seize the island, by force if necessary.

It tries to keep Taiwan isolated on the world stage and opposes countries having official exchanges with Taipei.