The US Federal Bureau of Investigation (FBI) is warning computer users to be wary of unsolicited email messages trying to raise money to help victims of last week's massive earthquake in China's Sichuan province.

The scam emails offer free vacation trips to the largest donors and may use fake logos of real online payment services in order to trick their victims, the FBI said. Similar scams followed tragedies such as Hurricane Katrina, the Virginia Tech shootings and the September 11 terror attacks on the US, the FBI said in an advisory.

The 7.9-magnitude earthquake struck on May 12, with its epicentre about 45 miles west of Chengdu. More than 41,000 people are confirmed dead after the disaster, and hundreds of thousands more have been injured.

Scammers are sending emails, some of them extremely long and filled with personal anecdotes, using titles such as 'Help me', 'Help me please. Read through the letter' and 'Last hope. Help me please', according to Sam Masiello, director of threat management with security vendor MX Logic. He has blogged about the scams here.

The emailers try to start a correspondence with the victim and then try to arrange a money transfer, he said. "This is one of your classic 419-type scams," he said.

MX Logic is intercepting several thousands of these scam emails each hour and has also seen some messages that contain malicious Word attachments, which are used to install unauthorised software on the victim's computer.

Criminals have also reportedly hacked into the Red Cross' China relief website and opened fraudulent bank accounts to siphon off relief funding.

"With every tragedy that's out there, it happens," Masiello said. "The human side of me hopes that they won't, but the security side of me knows that they will."