SINGAPORE-BASED taxi-booking app GrabTaxi has raised additional funding, which it will use to hire more tech staff and expand its market.

Founder Anthony Tan did not disclose the amount of investment, but said it was an eight-figure sum.

Vertex Venture Holdings was the principal investor in the funding round, he said, at a briefing at the M Hotel yesterday.

GrabTaxi, which was founded in Malaysia in 2011, is used by 250,000 people in 12 cities in Malaysia, Thailand, Philippines and Vietnam, as well as in Singapore.

Commuters typically get taxis within a minute of activating the app. They can also see the cabs in their area, pick the one closest and monitor its progress as it gets nearer.

A fare estimate is given as well.

Mr Tan said the app is the most widely used third-party taxi-booking mobile app in the five countries in which it operates.

It has been downloaded more than a million times and more than 20,000 cabbies are registered with it, with one booking made every two seconds.

He added that with the app, taxi drivers can increase their earnings by between 30 and 300 per cent each month.

Mr Tan also noted that the app takes some of the risk out of using a cab: "It's not so important in Singapore but in other countries, single women take a risk when they get into a taxi.

"With our app, they can send text messages or e-mail so that their loved ones and friends know they are safe and are on the way to their destinations."

Vertex initially invested in the start-up last September, said its chief executive, Mr Chua Kee Lock, who added that it is pouring in additional funds because the firm has proven itself.

Said Mr Chua: "They've expanded so quickly since then and we've been impressed with Anthony, who is hungry to succeed and who wants to build a lasting enterprise."

Mr Tan said the funding will help the firm take on more data analytics specialists to study passenger usage and traffic patterns.

The start-up takes a three, five or 7 per cent commission depending on factors such as the distance of each ride and the time of day.

The greatest challenge to GrabTaxi is the "hand", said Mr Tan.

"Putting up your hand and hailing a taxi is our greatest challenge. Every day, we focus on how to 'cut off' this hand and convert people to using their smartphones, to click on our app."

The company is a for-profit social enterprise, said Mr Tan, who is part of the Tan family that owns Tan Chong Motors.

"We want to help taxi drivers earn more money. They have a tough life fighting for customers and having to pay rental for their taxis. Our app helps them do this," he said.

One way to help taxi drivers is to make them feel comfortable using the app. In Singapore, the app is available in Chinese and Malay, as well as in English.

In other countries, GrabTaxi employees can speak the local dialects used by the drivers so they can train them and get feedback.

The mobile app is available for Apple, Android, Windows and BlackBerry devices.