Apple and Google collect smartphone users' location information as part of their race to build massive databases, The Wall Street Journal reported on Friday after analyzing data and documents.

According to the report, security analysts with the newspaper found that Apple's iPhone and smartphones running Google's Android operating system regularly transmit users' locations back to the two companies respectively, which is part of their race to build databases capable of pinpointing people's locations via smartphones.

A report by research firm Gartner indicated that the market for location-based services is expected to rise to 8.3 billion U.S. dollars in 2014 from the current 2.9 billion dollars.

In the case of Google, a security analyst with The Wall Street Journal said an HTC Android phone collected name, location, signal strength of any nearby Wi-Fi networks, and a unique phone identifier every few seconds and transmitted the data to Google at least several times an hour.

"All location sharing on Android is opt-in by the user," Google said in a statement to technology blog site All Things Digital, in response to the concern that how Android system uses location information.

"We provide users with notice and control over the collection, sharing and use of location in order to provide a better mobile experience on Android devices. Any location data that is sent back to Google location servers is anonymous and is not tied or traceable to a specific user," said the statement.

Worries on the iPhone tracking issue surfaced on Wednesday after two British researchers announced at a technology conference in California that iPhone has been collecting users' location information and storing the data for extended periods of time.

The researchers said starting on June 21 2010, after the release of iOS 4 mobile operating system, iPhones began logging and storing location information in a file, which shows the users' latitude and longitude and is timestamped to the second. They noted the information is not encrypted on the phone or on the iPhone backups made by iTunes and the file is also persistent, transferring itself to a new iOS device when the old one is replaced.

They added they had no evidence that the file was being transmitted to Apple.

On Thursday, U.S. congressman Edward Markey reacted angrily to the news in a letter to Apple CEO Steve Jobs, which is posted on Markey's official website.

Markey asked Jobs to make a response within 15 business days or no later than May 12, saying "Apple needs to safeguard personal location information of its users to ensure that an iPhone doesn't become an iTrack."

Apple has made no comment on the issue so far, but a letter it sent to U.S. Congress last July came under spotlight. In the letter, Apple said it collects Wi-Fi and GPS information when the phone is searching for a cellular connection and gathers the data to help build a "database with known location information."