Mexico City - Five months after a large earthquake shook Mexico City, the capital is better prepared to deal with future tremors and is focused on tightening up building codes and improving its emergency response, said Mayor Miguel Angel Mancera.

Improving air quality in the city of over 21 million people and securing enough water to supply the population remain chronic problems, he said, as do cleaning up dirty industries and switching to greener energy supplies.

"It's a city that has to become more resilient to earthquakes ... the city is responding well, it's much better prepared," Mancera told the Thomson Reuters Foundation.

"The city's strengthening itself ... economically, preparing funds, creating insurances, but also implementing stricter construction rules because we know it could shake again."

Mexico City residents had just a few seconds warning of the 7.1 magnitude tremor that struck the nearby state of Morelos on September 19 killing more than 330 and damaging 11,000 homes in the capital and surrounding states.

Demolishing damaged properties and rebuilding were slow processes, said Mancera, adding the city still needed to boost its civil protection and was writing a new emergency response plan drawing on its experiences of September's quake.

"The reconstruction is not fast - it is not from one day to another. I said that this reconstruction could take the city five or six years," Mancera said on the sidelines of a Women4Climate conference in the city on Monday.

Improving air quality remains a key priority, said Mancera in an interview held in the city center museum, as Greenpeace activists outside carried a banner reading "In Mexico City the air is killing us." Cleaning up industry remains a major hurdle, as does plugging the leaks responsible for the loss of at least 35% of the city's water as it travels through 12,000 km (7,500 miles) of pipes, he said.

Engineers are drilling 2-kilometer-deep wells to find new water sources, said Mancera, who noted greater investment in the network and more water reuse could alleviate shortages.

Despite the lack of water in the capital - where aquifer depletion is causing subsidence - Mancera dismissed any possibility that Mexico City could run dry and face its own "day zero" like South Africa's Cape Town.

"I don't think we'll reach 'day zero' but we need more investment and we also need to reuse water - it's another very important point that should be on government agendas," the Mayor said.