At the same time the People's Republic of China entered the conflict after issuing several warnings to the United Nations. On 19 October 1950, large formations of Chinese troops, dubbed the People's Volunteer Army (PVA), secretly crossed the border and into North Korea. One of the first Chinese units to reach the Chosin Reservoir area was the PVA 42nd Corps, and it was tasked with stopping the eastern UN advances. On 25 October, the advancing ROK I Corps made contact with the Chinese and halted at Funchilin Pass (), south of the Chosin Reservoir. After the landing at Wonsan, the US 1st Marine Division of the X Corps engaged the defending PVA 124th Division on 2 November, and the ensuing battle caused heavy casualties among the Chinese. On 6 November, the PVA 42nd Corps ordered a retreat to the north with the intention of luring the UN forces into the Chosin Reservoir. By 24 November, the 1st Marine Division occupied both Sinhung-ni () on the eastern side of the reservoir and Yudami-ni () on the west side of the reservoir.