HONG KONG — China appears to have received help on Saturday from an unlikely source in its fight against tools that help users evade its Great Firewall of internet censorship: Apple.

Software made by foreign companies to help users skirt the country’s system of internet filters has vanished from Apple’s app store on the mainland.

One company, ExpressVPN, posted a letter it had received from Apple saying that its app had been taken down “because it includes content that is illegal in China.”

Another tweeted from its official account that its app had been removed.

A search on Saturday showed that a number of the most popular foreign virtual-private networks, also known as VPNs, which give users access to the unfiltered internet in China, were no longer accessible on the company’s app store there.