MUMBAI, INDIA - Ruthless gunmen, terrified guests, pitch darkness and a fear of harming hostages posed huge challenges to commandos charged with ending Mumbai's hostage crisis, their commanders said Friday.

A masked leader of India's crack Marine Commando Force, known as MARCOS, told reporters that his men had been severely hampered by the sheer number of people still inside the Taj and Oberoi/Trident hotels when they moved in to flush out the militants.

"We could have got those terrorists but for so many hotel guests," he said.

Dressed in combat black, with his face completely covered by a mask and reflective sunglasses, the commando said his men had had to literally feel their way through the hotel corridors and rooms in complete darkness.

Asked to give some details about casualty numbers, he said it had often been impossible to differentiate between dead bodies, the injured and people simply pressing themselves to the floor in terror.

"When an exchange of fire takes place in darkness and there are bodies strewn all over, and blood all over, you're actually not looking who is injured or killed.

"You're just looking for someone with lots of weapons on him," he said.

Security officials said the men - described by eyewitnesses as "just like boys" dressed in cargo pants and T-shirts with rucksacks across their shoulders - were a highly motivated and determined group.

Split into small groups, they created panic Wednesday night by attacking locations across Mumbai before focusing their assault on the two five-star hotels and a separate office-residential building housing a Jewish centre.

"They were the kind of people with no remorse," the masked commando said. "Anybody and whomsoever came in front of them they fired."

Lieutenant General S. Noble Thamburaj, who heads the Indian army's southern command, said his men had needed to show enormous patience, even when dealing with a lone remaining and wounded gunman in the Taj Hotel.

The militant was continuously "moving between two floors" of the building. "He has cut off lights and sometimes he gets holed up" in one or other of the rooms, said Thamburaj.

"We heard a sound of a lady and a gentleman. So it is possible that this terrorist has got two or more hostages with him. It is also possible that there is more than one terrorist," he added.

Thamburaj said a large number of hotel rooms had been locked from the inside and the occupants refused to answer even when his men identified themselves.

This made it near impossible to be sure which rooms might contain gunmen - with or without hostages - or just frightened guests.

"The life of hostages... was of great importance to us. We told the commandos not to rush... not be under pressure from the media or citizens when we are in the final stages of the operations," he said.

Security personnel also had to use sniffer dogs to ensure bodies were not booby-trapped before removing them and declaring the area "sanitised," added Thamburaj's junior officer, Major General R.K. Hooda.

While most of the guests and the staff had been evacuated, Thamburaj did not rule out the possibility of people still being trapped.