Fires erupted and dark plumes of smoke rose from enclaves still occupied by the militants as the air force staged bombing runs to support ground troops struggling to dislodge the fighters from entrenched positions, AFP journalists at the scene said.
MG520 attack helicopters and FA50 fighter jets were used in the raids, while sustained bursts of automatic gunfire could be heard in the distance, indicating the intensity of the fighting.
Television footage showed the soldiers bidding goodbye to their families before being flown to the conflict zone.
Hundreds of militants -- supported by foreign fighters -- rampaged through Marawi, the largely Christian Philippines' most important Muslim city, on May 23 waving black flags of the Islamic State (IS) group.
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President Rodrigo Duterte declared martial law in the entire southern region of Mindanao to counter the attack, which he said was part of a plan by IS to establish a base in the country.
The military has said eight foreign fighters from Chechnya, Yemen, Malaysia and Indonesia were among the militants killed in the Marawi fighting.
The overall death toll rose to 329 with 310 -- 225 militants, 59 soldiers and 26 civilians -- killed in the conflict, according to government figures.
The 19 others deaths came from those displaced by the fighting, said Mujiv Hataman, the governor of a Muslim autonomous region in the south.
Hataman said the deaths among the evacuees were caused by severe dehydration from diarrhoea.
"Our forces are moving towards the heart of the enemy," regional military spokesman Jo-ar Herrera told reporters in Marawi on Saturday, referring to the heavy fighting under urban conditions.
"It's the centre of gravity. This is where the location of their command and control, the leadership of the enemy."
Ground commanders estimate "more than 100" militants are still holding out in at least four villages in Marawi, military spokesman Brigadier General Restituto Padilla said in Manila.