The Martin Aircraft Company is proving to be a highly volatile investment, with the New Zealand jetpack maker's stock price rocketing one minute and crashing back to earth the next.

The Christchurch-based company's shares, which listed on Australia's ASX at A40c last week, opened at A$1.82 yesterday before rallying to a record A$3.15, giving the firm a market capitalisation of A$769.5 million ($798.7 million).

That's a mind-blowing valuation for a loss-making, pre-revenue business, which doesn't expect to sell its first jetpack until the second-half of next year.

But after hitting the record high the stock fell back to close at A$1.65 last night, valuing the company at A$403.1 million. Some 7.4 million shares changed hands yesterday.

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At the A$3.15 high, founder Glenn Martin's 15.9 per cent stake in the business was worth A$122.4 million.

In the lead-up to the firm's oversubscribed initial public offering, which raised A$27 million, brokers warned the company was at the high-risk end of the investment spectrum.

It's hard to imagine large numbers of the aircraft - the recreational version of which is expected to cost US$150,000 (almost $200,000) - buzzing around. But the share price suggests there's a fair few investors who are willing to take a punt.

Daniel Metcalfe, a senior client adviser at sharebrokers OMF, said speculation was driving the "extreme volatility" in the stock.

"I wouldn't touch [the stock] with a barge pole," Metcalfe said.

The company expects to begin deliveries of its First Responder aircraft - developed for police, search and rescue and other government uses - next year.