SEOUL (BLOOMBERG) - South Korea urged the United States to "refrain from taking excessive measures" after the State Department raised its travel advisory on the Korean city of Daegu, where most of the nation's coronavirus cases are centred.

Foreign Minister Kang Kyung-wha spoke to US Deputy Secretary of State Stephen Biegun by phone, according to a statement from the South Korean foreign ministry.

She said that while the virus is spreading in the country, it is concentrated in a specific region and the government is making an all-out effort to prevent further infections, the ministry said.

The call took place just hours after the State Department raised its travel advisory on South Korea's Daegu to Level 4, its most severe grade.

The department urged citizens to not travel to the city, citing risks of community transmission and local quarantine procedures.

On Feb 24, it issued a Level 3 advisory for South Korea, advising citizens to avoid non-essential travel to the country.

Meanwhile, South Korean President Moon Jae-in asked North Korea for "healthcare cooperation" at an event to mark the anniversary of the nation's independence movement under Japanese rule 101 years ago.

"The lives of the Korean people will be safer when the two Koreas can respond together when infectious diseases spread among humans and animals, and jointly cope with disasters and catastrophes in border areas, and climate change on the Korean Peninsula," he said in a speech.

The South Korea Foreign Ministry on Sunday summoned Vietnam's ambassador to Seoul, Mr Nguyen Vu Tu, to "express regret" over the diversion of an Asiana Airlines plane from Noi Bai International Airport in Hanoi, its original destination, to another airport on Saturday.

Asiana Airlines officials told Yonhap News Agency they believed the move was related to the coronavirus outbreak in South Korea.