Financial Secretary John Tsang Chun-wah has admitted the government had "no experience or psychological preparation" for the "unprecedented" Occupy Central campaign. Writing in his latest weekly blog, the city's No 3 official said he "did not sleep well" and worried about the city-wide civil disobedience protests escalating. "The rapid pace of developments over the past week was completely beyond everybody's expectations," wrote Tsang. "It's hard not to be concerned that more serious chaos would happen ... To be honest I persistently didn't sleep well. "Undeniably, the transformation of the mass movement is unprecedented. The government, political parties, community groups, the media and the public have no experience or psychological preparation to face this situation, making it all the more difficult to resolve the standstill." Tsang added: "Groups of different classes, backgrounds and interests in society have a completely different understanding and judgment of the event, with diametrically opposite reactions, making it difficult to predict how events will develop in future." The confrontation between pro- and anti-Occupy groups in Mong Kok "further deepened our worries", Tsang said. "It led to fears that ... more serious matters would be triggered. "This event is a grave test for all Hong Kong people. Its handling will require everyone's wisdom and patience." The financial secretary's article came ahead of his visit to the annual conference of the International Monetary Fund and the World Bank in Washington. Tsang said he had considered whether to cancel the trip but decided to go in order to explain the local situation in person. "This US visit is a timely opportunity to explain to overseas friends Hong Kong's situation, to respond to their queries and to clear any misunderstanding," he wrote. "The Heritage Foundation has, for 20 years, ranked Hong Kong as the freest economy in the world. I hope to make use of this opportunity to brief the foundation on Hong Kong's latest [situation] to maintain foreign investors' confidence in Hong Kong." During his trip, Tsang will meet US Federal Reserve chairwoman Janet Yellen. Speaking to the media at the airport as he was about to depart, Tsang again urged protesters to disperse.