Officials in the Japanese city of Yokohama were left red-faced on Wednesday after mistakenly announcing the launch of a North Korean missile to 40,000 followers on Twitter. The city, south of Tokyo, prematurely fired its tweet just before noon (0300 GMT), announcing \"North Korea has launched a missile\" with blank spaces to indicate the exact time. \"We received a call from one of our followers who had noticed the mistake. We had the tweet ready and waiting, but for an unknown reason it was dispatched erroneously,\" said a city official. The city retracted the tweet about 20 minutes later and apologised to followers of @yokohama_saigai, the official said. Japan is on full alert ahead of an expected mid-range missile launch by North Korea, with Patriot missiles stationed in its capital to protect the 30 million people who live there. In addition to PAC-3 batteries, Aegis destroyers equipped with sea-based interceptor missiles have been deployed in the Sea of Japan (East Sea). Twitter is wildly popular in Japan, where the ideograph and pictograph-based language is well-suited to the 140 character limit, allowing much more information to be imparted than alphabetic languages like English.