NEW YORK - A radioactive leak at a New York nuclear power plant has dramatically increased the levels of radioactivity in the City's groundwater, prompting officials to order an investigation into the case, Governor Andrew Cuomo stated.

Cuomo made the announcement on Saturday, stating he became aware of “alarming” levels of radioactivity in the groundwater below the facility the day before, after water contaminated with tritium leaked from a reactor.

While the facility reported that the contamination has not migrated off site and did not pose an immediate public health threat, Cuomo said that the incident requires a full investigation.

"Our first concern is for the health and safety of the residents close to the facility and ensuring the groundwater leak does not pose a threat," Cuomo said.

Three monitoring wells at the Indian Point plant in Buchanan, about 40 miles (65 km) north of New York City on the east bank of the Hudson River, were showing high levels of radioactivity, he said.

At one well, radioactivity spiked by nearly 65,000 per cent, from 12,300 picocuries per liter to more than 8 million picocuries, the Governor warned.

Cuomo has urged the Nuclear Regulatory Commission to shutter the plant because of doubts over the safe evacuation of the area in the event of an accident.

The governor said the plant's operator, Entergy Corp, has informed him the contaminated water has not moved off the site and poses no public health risk at the moment. Cuomo said he has directed the State’s environment and health departments to investigate the leak.

"Our first concern is for the health and safety of the residents close to the facility and ensuring the groundwater leak does not pose a threat," he stated.

Entergy also released a statement, stating the tritium likely reached the ground at Indian Point during recent work at the site.

"While elevated tritium in the ground onsite is not in accordance with our standards, there is no health or safety consequence to the public, and releases are more than a thousand times below Federal permissible limits," the company said.

According to Cuomo’s letter ordering the state investigation, Indian Point has had problems with the release of radioactive water in the past, and this time the levels of radioactivity reported by the company are worse than before.

On May 9, 2015, a unit at the plant was shut down following a transformer failure and fire, in an incident that sent smoke spewing from the plant.

Despite the incident, the plant remained operational and the Nuclear Regulatory Commission (NRC) said it posed no threat to the public.