TOKYO -- The coronavirus outbreak remains at an initial stage in Japan, an expert panel under the health ministry said Sunday, choosing not to raise the country's alert level to allow for a more aggressive response.

"The government is still able to track down infection routes to a certain degree," said Takaji Wakita, chief of the National Institute of Infectious Diseases.

The health ministry had hoped for an upgrade to the next alert level, which signals a rapidly growing outbreak with high domestic transmission rates. Such a move would let the ministry switch focus from screening overseas arrivals and tracking infection routes to catching homegrown cases early on and boosting treatment capacity.

"It was a difficult decision, but we are still at the beginning of an outbreak, and the virus is not yet prevalent," a member of the panel said.

Japan had 53 cases of the coronavirus as of Sunday, apart from those linked to a cruise ship docked in Yokohama. Despite the decision Sunday, the ministry remains concerned about the increase in patients with no direct ties to China, the epicenter of the outbreak.

"We will bolster measures at home in anticipation of an eventual surge in cases," a ministry official said.

One public health expert at Jikei University School of Medicine told Nikkei that he thinks the outbreak is already at the next phase, with infections likely spreading in the country. "The worst-case scenario is where the one-day increase keeps going up, say, from 10 today to 20 the next day," said professor Mitsuyoshi Urashima. "Once this happens, the government could invoke an emergency law and bar people from going outside."

"The best-case scenario is where most infected people recover with mild to no symptoms, which will increase the number of people with immunity to the virus," Urashima said.