Unprecedently

Despite the fact that these women were starved and badly clad and deprived of the comforts of home, the death rate of the infants dropped steadily to an unprecedently low mark.

Source: wiktionary

Chingchou Prefecture, comprising several counties in Hupei Province, suffered a disastrous three years, and its tribulations were not unique. Massive floods rolled over one county in 1830, drowning hundreds of thousands and befouling the rice fields with sand. The dikes restraining the Yangtze River collapsed in a neighbouring county in 1831 and half the population starved to death. In 1832, the prefectural capital suffered a severe famine while, elsewhere in Chingchou, cholera struck down tens of thousands and the normal autumnal floods were unprecedently severe.

Source: wiktionary

The 72‐year‐old Mr. Brezhnev, speaking in the Kremlin's Palace of Congresses, reserved his toughest language for the Chinese, whose invasion of Vietnam began Feb. 17. He called it an “unprecedently brazen bandit attack” in which the Chinese rulers “revealed fully to the whole world the perfidious, aggressive essence of the great‐power policy pursued by them.”

Source: wiktionary

In a letter to U.N. Secretary General Javier Perez de Cuellar, Gorbachev said that although it produced no practical results, the Reykjavik summit had at least raised the cause of nuclear disarmament to "an unprecedently high plateau."

Source: wiktionary