The messaging service WhatsApp has been disrupted in China as the government steps up security ahead of a Communist Party meeting next month.
At times, it has been completely blocked and only accessible via virtual private networks which circumvent China's internet firewall.
WhatsApp is Facebook's only product allowed to operate in mainland China.
The BBC's China based correspondents said the WhatsApp messaging service started going offline more than a week ago.
A test of its services on Tuesday showed users in China could not send video messages or photographs to people outside China.
The disruption follows restrictions on WhatsApp video chats and photographs in July, which were later lifted.