U.S. health authorities are warning about the use of e-cigarettes after reports of multiple deaths from mysterious lung illnesses tied to vaping. 

The Centers for Disease Control and Prevention (CDC) said on Friday that there are at least 450 cases of vaping-related lung illnesses in 33 states now under investigation by state and federal health officials. 

At least two deaths have been reported to the CDC, the agency said in a statement. It said other cases of lung illness are being investigated "to determine whether they are linked to e-cigarette use and have similar clinical features." The CDC is also looking back at older cases and said states are in the process of classifying possible cases.

Three deaths have been reported so far, one each in Oregon, Illinois and Indiana, Bloomberg reported on Friday. The Washington Post reported that there have been five deaths.

According to the CDC, many of the people who became ill had used products containing THC, while others had used products with both nicotine and THC. A smaller group reported using nicotine-only products. The CDC said there has been no evidence of infectious diseases in these patients, "therefore lung illnesses are likely associated with a chemical exposure."

However, the CDC said it was too early to pinpoint a single product or substance common to all cases.

"We are committed to finding out what is making people sick," Robert Redfield, director of the CDC said in a statement. "All available information is being carefully analyzed, and these initial findings are helping us narrow the focus of our investigation and get us closer to the answers needed to save lives."

The CDC also said people "should consider not using e-cigarette products," and those who do should monitor themselves for symptoms such as cough, shortness of breath, chest pain, nausea, vomiting, abdominal pain and fever. It also warned people about buying the e-cigarette products off the street.

A spokesman for e-cigarette maker Juul Labs said the company has been monitoring the situation closely.

"To be clear, the ingredients of our products do not include THC, any compound derived from cannabis, or vitamin E compounds like those found in THC products," the spokesman said in an email. "We appreciate the work of the CDC, FDA and other public health authorities and are confident that they will get to the bottom of this issue."

Altria  ( MO) bought a 35% stake in Juul last December for $12.8 billion.