Instant messaging service WhatsApp has been largely blocked in China, the media reported.

The Open Observatory of Network Interference (OONI), a global observation network for detecting censorship, surveillance and traffic manipulation, suggested on Monday night that Chinese internet service providers started blocking access to WhatsApp on September 23, reports CNN.

Public reports on Twitter indicated that WhatsApp, which is owned by the US-based social media giant Facebook, became inaccessible for some people on September 19.

Over the last few months, there were a number of WhatsApp disruptions in China.

However, WhatsApp has not made an official announcement on the development.

China has already blocked access to a number of internet companies, including Facebook, Instagram, Twitter and Google.

Some people access these services through virtual private networks (VPN), or with tools that disguise internet traffic to circumvent censorship. But the Chinese government has launched a crack down on VPNs this year.

According to Timothy Heath, senior international defence research analyst at the RAND Corporation, the Chinese government does not like that WhatsApp uses strong encryption.

"The government wants to monitor internet communications, and therefore it's trying to steer its people to use technology that can be accessed and monitored by the government," Heath told CNN.

Earlier this month, WeChat, a popular chat service in China, notified users of its policies to comply with government requests for information.