MUMBAI - India's top automaker Tata Motors unveiled a new version of what was once billed as the world's cheapest car Wednesday, in a bid to reverse a slump in sales.

The jellybean-shaped Nano, which sold for around $2,200 when its first edition went on the market in 2009, has seen sales drop by more than 27% in the last year and Tata's recently-retired supremo admitted the car had an image problem.

The compressed natural gas (CNG)-fuelled version of the Nano unveiled on Wednesday is expected to hit showrooms within the next 90 days, the company said.

Tata Motors did not disclose the CNG Nano price, but said it would be announced soon.

"This (CNG) is the first major variant for the Nano since its launch," auto analyst Mahantesh Sabarad of Fortune Equity Brokers said.

Sabarad said the CNG version is being introduced to "give customers a better choice" but may take away its "affordability" tag.

It was not immediately clear whether the Nano would retain its title as the world's cheapest car.

In an interview shortly before his retirement last December, the company's long-time chairman Ratan Tata said it had been a mistake to market the Nano merely on its low-price, saying "various stigmas have been attached to it."

Sales of the part-plastic Nano fell 27.7% in the fiscal year to March 2013, to 53,847 units, according to company data.