BENGALURU/NEW DELHI (Reuters) - Tech enthusiasts across India joined hands to help those left stranded by deadly flooding in the southern city of Chennai, using social media to crowd-source information to supply food, top up mobile phone credits and offer refuge.

Residents wade through a flooded street as they evacuate their homes in Chennai, in Tamil Nadu, India, December 3, 2015. REUTERS/Anindito Mukherjee

Incessant rainfall in India’s fourth most-populous city has cut off more than three million people from basic services and disrupted power supplies, with the authorities under fire for slow relief and rescue operations.

Volunteers and companies have responded by using online tools such as Google documents and social networks like Facebook and Twitter to organize their own crisis response, with some setting up dedicated online resources to help others in need.

“We are passing rescue requests to government officials and local people,” said Krish Ashok, part of a team running Chennairains.org, which lists verified details of those offering shelter, water and clothing.

The Indian military has struggled to evacuate thousands of residents stranded in and around Chennai. Heavy rains in Tamil Nadu state have killed at least 269 people and critically injured 1,000.

Mobile and internet services, though intermittent, have become the key mode of communication between those offering and seeking aid in the coastal IT outsourcing hub.

Practo, a company that connects patients to doctors, issued a public Google document with a list of 57 doctors available for consultation. The list was being updated by a five-member team.

“We are checking doctors’ availability hourly due to the connectivity issues. We’re also adding details of doctors who’ve reached out and volunteered to help,” a Practo spokesman said.

On social media, citizens used hash tags such as #ChennaiRainsHelp to share helpline numbers, offer free food and drugs and even arrange conference calls for those out of credit on their mobile phones.

Ammar Kanchwala, a Hyderabad-based IT executive, said he had used his own funds to add calling credits to about 50 mobile phone users who were stranded.

Sriharan Balan, a 25-year-old travel consultant in Chennai, was using Facebook to reach out to those in need and supplying them with home-cooked food. “These are all my people. Obviously, I need to help them,” he said.

Three software developers also used data from several sources to build a dynamic map that shows flooded roads in the city.(bit.ly/1TtRB2e)

While 18,000 people have been evacuated from rooftops and outlying villages, many remain in dire need of basic supplies.

Ola, India’s leading online taxi firm that last week worked with fishermen and professional rowers to co-ordinate boat rescues, said it was running temporary homes that were equipped with relief supplies.