A man has been jailed in Hong Kong for burning the national flag, in the first sentence of its kind.Zhu Rongchang, 74, a farmer from mainland China, was sentenced to three weeks in prison over the 22 July incident.He had denied the charge, saying he was exercising his right to free speech. He burned the flag in Golden Bauhinia Square in central Hong Kong, in what he said was a protest against the government in Beijing.Mr Zhu is the third person to be charged under the flag-burning law, which came into effect in 1997 when Hong Kong was returned to China, and the first to be jailed.According to the South China Morning Post, Magistrate Jason Wan Siu-ming said that while freedom of speech was a universal value "pursued by all people", every freedom was restricted "in some way"."No freedom comes without restrictions. I can appreciate the defendant's trail of thoughts but his way of expression breached the Hong Kong laws and therefore he is guilty," the newspaper quoted him as saying.