The company did not immediately return requests for confirmation.
The reports came amid pro-democracy protests in Hong Kong, where many have posted photos and videos, including of Hong Kong police firing tear gas at demonstrators.
Many of the photos were labeled with the hash tag "Occupy Central," a phrase that was blocked on Sunday on Weibo, China's version of Twitter. It had been allowed earlier in the day.
The website www.blockedinchina.net also indicated that Instagram was blocked across China, including in Beijing and Shenzhen.
If the site was blocked in China, that would not prevent users in Hong Kong from posting on social media, nor users in other countries viewing the images.
© Thomson Reuters 2014
Get your daily dose of tech news, reviews, and insights, in under 80 characters on Gadgets 360 Turbo. Connect with fellow tech lovers on our Forum. Follow us on X, Facebook, WhatsApp, Threads and Google News for instant updates. Catch all the action on our YouTube channel.