Prime Minister Datuk Seri Najib Razak is "cautiously optimistic" of a "good victory" in the upcoming general election -- which is expected to be the most heated and contested general election in the country's history.

"I’m cautiously optimistic that we’ll have a good victory. Two-thirds is achievable but I also realise that in an election anything can happen, so that’s why I say I am cautiously optimistic,” said Najib in an interview with the Financial Times earlier (on Wednesday night).

“Investors are looking for a strong mandate for the current government. If we should, or rather when we get a good result, you will see an unprecedented boom in the stock market. I’m quite confident of that.”

Economists have so far acknowledged and welcomed the government's efforts in growing the economy -- which saw the country's gross domestic product (GDP) registered a better-than-expected growth of 5.6 per cent in 2012.

However, economists were concerned about the country's debt to GDP ratio of 51 per cent. They also feel that there's more room for growth in terms of government revenue.

“I will look at the tax structure, definitely, because we need to enhance the revenue base... The government revenue base has to be predicated on a much stronger footing,” said Najib when asked if he would be introducing goods and services tax.

On the manifesto presented by Pakatan Rakyat, Najib told the Financial Times that the manifesto is "not credible".

“I think it is too risky to put faith in a coalition that does not have a clear sense of direction that they want to take the country in,” he said.

Last year, Najib surprised many political observers when he changed Umno's constitution -- which ultimately makes it easier to challenge the leadership.

“I’ve made Umno more democratic, more inclusive. Of course by doing that I’m putting myself at risk. But I believe that what were doing is good for the country and good for the party.”