Indian authorities have said they cannot ignore an estimate by some non-governmental organizations (NGOs) that over 11,600 people may be missing in the monsoon floods which devastated the northern state of Uttarakhand last month.

"The government estimates that more than 4,000 people are missing, but the number could be much higher. The estimate by some NGOs that about 11,600 people may be missing cannot be ignored," National Disaster Management Authority's Vice Chairman Shashidhar Reddy told the media.

"There are three categories -- pilgrims, local residents and those who work as labor. I think an assessment of these numbers will have to go into the official figures," he added.

Though so far more than 120,000 people, who were stranded in the difficult terrains of the hilly state, have been rescued, the Indian Army and Indian Air Force have been continuing evacuations by air despite incessant rainfall.

Monsoon floods swept through Uttarakhand on June 16, triggering landslides and washing away towns and roads, in which thousands were killed. The state, popular for its holy Hindu shrines and rivers, received the heaviest rainfall in the last 60 years this year.