(CNN) -- A lava surge began Friday in the crater of the rumbling Colima
                  Volcano, leading experts to forecast the smoldering summit would stage a
                  "low-intensity" emission of molten rock rather than an explosive eruption
                  as some had predicted.

                  The appearance of the lava, detected by researchers flying in a helicopter over
                  the 13,000-foot (3,820-meter) peak, forced authorities in southern Colima state
                  to delay plans to let residents of an evacuated village return to their homes.

                  "The developments indicate that a low-intensity lava flow has begun.... If it
                  continues, it would overflow onto one of the volcano's slopes," the state
                  government said in a press statement.

                  Such a flow would endanger the village of Yerba Buena, on the volcano's
                  southern flank about five miles (eight kilometers) from the crater.

                  All 140 residents of the village were evacuated Wednesday after the volcano
                  signaled an impending eruption stronger than any seen in decades.

                  Friday, as the Colima volcano still threatened to erupt, four villages were
                  evacuated by civil defense authorities, an official told local radio.

                  Maritza Oropeza, civil defense spokeswoman in the Pacific coast state of
                  Colima, 400 miles (650 kilometers) northwest of Mexico City, told Radio
                  Red that 758 villagers were taken to shelters.

                  The Colima volcano is classified by the National Disaster Prevention Center
                  as the most active in Mexico and has erupted about 25 times in the past 500
                  years.

                  In 1913 a volcanic explosion shattered windows and showered ash in towns
                  several miles away.

                  However, geologists say that the current eruption will be more like a 1991
                  incident in which lava flows didn't reach the lower flanks of the peak.

                  No lava flow in recent history at the volcano -- also known as the Volcan
                  de Fuego, Spanish for Volcano of Fire -- has reached towns or roads on
                  the lower flanks.

                  Residents of two small villages on the northern reaches of the volcano in
                  neighboring Jalisco state were also evacuated Wednesday. They will be
                  allowed to return to their homes, authorities said. The release of lava through
                  the crater may reduce pressure building up under the peak and reduce risks
                  to those hamlets.

                  By Thursday the lava had pushed aside blocks of old volcanic material
                  measuring 50 meters by 20 meters (165 feet by 65 feet) that were deposited
                  by previous eruptions and had been obstructing the volcano's ducts.

                  Smaller blocks of solidified lava have been tumbling down the slopes over
                  the past few days, as the pressure increased.

                       The Associated Press and Reuters contributed to this report.