More than 450,000 people have signed two petitions demanding that the Indian government declare a climate emergency as severe heatwaves and crippling water shortages grip the country.

Inspired by teenage Swedish climate activist Greta Thunberg, 16-year-old student Aman Sharma launched a petition on Change.org in May after noticing that every successive year was getting hotter, drier, thirstier and more polluted, he said.

"I started this campaign to put pressure on the government because if we keep silent right now then it's going to affect our survival in the future," he told the Thomson Reuters Foundation on Friday as his petition gathered more than 170,000 signatures.

His other demands to the environment ministry include increasing the country's green cover and meeting pledges made under the 2015 Paris climate agreement to try to limit a rise in global warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit).

The Ministry of Environment, Forests and Climate Change did not respond to repeated requests for comment.

With backing from several film personalities including actress Nathalie Kelley from U.S. TV soap "Dynasty" as well as some Bollywood names, Sharma said his next aim was to draw Hollywood environmentalist Leonardo DiCaprio's attention.

On Wednesday, DiCaprio posted a photo on Instagram of women in the southern city of Chennai drawing pots of water from a near empty well, capturing the daily struggle of thousands.

Chennai has been in the global spotlight since its four main reservoirs dried up earlier this month, largely because of poor monsoons in 2018, forcing residents to ration the use of water.

The city was one of 21 cities predicted to run out of ground water by 2020, government think-tank NITI Aayog said in a report published last year.

It warned that India faced the worst long-term water crisis in its history, with 600 million people - nearly half of India's population - at risk of facing acute shortage.

In the north, a heatwave has killed at least 36 people this year, with New Delhi recording its highest-ever temperature of 48 degrees Celsius (118 Fahrenheit).

Jitendra Sharma, a popular Mumbai-based Instagram influencer, started a similar petition this week which had nearly 300,000 signatures by Friday.

He said he was hopeful that the government would announce a climate emergency.

"It is the need of the hour," he said, citing other countries taking similar action.

In May Britain's parliament declared a symbolic climate change "emergency" in a nod to an increasing vocal activist movement particularly among young people in Europe.

While there is no single definition of climate emergency, environmentalist Chandra Bhushan said it was the act of placing climate change at the centre of policy and planning decisions.

"It means the Indian government will have to recognise we are in crisis, will have to set up an action plan," said Bhushan of the Delhi-based Centre for Science and Environment.

"We are in trouble. Even if the Indian government does not recognise climate emergency now, it is a matter of time that they will have to."