Because of this alert, USA government employees can not travel between cities after dark in much of the country.
The U.S. Embassy in Mexico City posted the notice on its website Wednesday for the popular coastal spot near Cancun and Cozumel on the Caribbean.
A State Department official did not elaborate on what the threat was. She assured the department would provide "important updates when information becomes available" but personnel must keep away "until further notice".
Meanwhile, officials in the Mexican state of Quintana Roo, where Playa del Carmen is located, have insisted that the city is safe. A day earlier, a shooting at a music festival in Playa del Carmen left three foreigners and two Mexicans dead.
"All tourism and economic activity in Playa del Carmen continues in a normal manner", the state government said, according to the Associated Press.
The U.S. Embassy in Mexico has issued a travel warning for a popular tourist hotspot, following a "security threat" alert and an explosion aboard a ferry last month. Mexican authorities are investigating the blast.More news: Peyton Manning Selling Ownership Stake In Papa John's
On March 1, an further explosive device was found on a different ferry, following the first explosion in February. More than 20 people, including foreign travelers, were injured. Travelers should contact the nearest U.S. Embassy or Consulate if they need assistance.
It said the USA consular agency there "will be closed until further notice".
"In Mexico alone, we've issued a number of recent security alerts as soon as we received information that travelers should know".
Last summer, the department also cautioned vacationers to be careful when drinking alcohol in Mexico. The state of Quintana Roo also comes with a Level 2 warning.
While these groups don't usually target tourists, the advisory says "armed clashes" between criminals and security forces can occur without warning and Canadians could be "caught in the crossfire". "While most of these homicides appeared to be targeted, criminal organization assassinations, turf battles between criminal groups have resulted in violent crime in areas frequented by US citizens".