Archaeologists have found two ancient Mayan cities hidden in the jungle of southeastern Mexico, and the lead researcher says he believes there are "dozens" more to be found in the region.

Ivan Sprajc, associate professor at the Research Center of the Slovenian Academy of Sciences and Arts, said his team found the ancient cities of Lagunita and Tamchen on the Yucatan peninsula in April by examining aerial photographs of the region.

Sprajc said the two cities reached their heyday in the Late and Terminal Classic periods (600-1000 AD). At each site, researchers found palace-like buildings, pyramids and plazas. One of the pyramids is almost 20 metres high.

They also found a facade featuring a monster-mouth doorway, which probably marked one of the main entrances to the center of the city. Photographs from the sites showed stone pyramids jutting out from beneath dense foliage.

"The entrance apparently symbolizes the entrance to a cave and to the underworld ... Someone entering through this doorway would have entered sacred precincts," he told Reuters by telephone from Slovenia on Friday.

Sprajc said his team mapped 10-12 hectares at each site, but the cities were probably larger.

"We elaborated a map but only of the religious and administrative centers of the two sites," he said, "that's only like downtown."

His team has not yet excavated the sites.

"There are dozens of sites that I already have seen on the aerial photographs," he added, noting that additional discoveries depend on further funding.

Last summer, Sprajc discovered another ancient Mayan city, Chactun, 10 km north of Lagunita and 6 km northwest of Tamchen.