In the 1830s, Gützlaff was persuaded by William Jardine of Jardine, Matheson & Co. to interpret for their ships' captains during coastal smuggling of opium, with the assurance that this would allow him to gather more converts. He was interpreter to the British Plenipotentiary in negotiations during the First Opium War of 1839–42, then magistrate at Ningpo and Chusan. He was appointed the first assistant Chinese Secretary of the new colony of Hong Kong in 1842 and was promoted to Chinese Secretary in August of the following year. In response to the Chinese government's unwillingness to allow foreigners into the interior, he founded a school for "native missionaries" in 1844 and trained nearly fifty Chinese during its first four years.