Yahoo has over 600 million users and is second in the search market
The Yahoo e-mail accounts of foreign journalists based in China and Taiwan have been hacked, according to a Beijing-based press association.
Rival Google has been involved in a high-profile row with the Chinese government following similar cyber-attacks against Gmail accounts.
The Foreign Correspondents' Club of China (FCCC) has confirmed eight cases of Yahoo e-mail hacks in recent weeks.
Yahoo said it condemned such cyber-attacks.
But the FCCC accused Yahoo of failing to update users about the situation.
"Yahoo has not answered the FCCC's questions about the attacks, nor has it told individual mail users how the accounts were accessed," a spokesman told the news agency.
Yahoo said in a statement that it was "committed to protecting user security and privacy".
Clifford Coonan, a reporter for the Irish Times, told the AFP news agency that he had an error message when he logged into his Yahoo account this week.
"I don't know who's doing it, what happened. They (Yahoo) haven't given any information, but it seems to be happening to journalists and academics in China, so that's why it's a little suspicious," he said.
China censorship has hit the headlines since the high profile cyber-attacks against the Gmail accounts of Chinese human rights activists in January.
The hacks led the search giant to redirect its traffic to an uncensored site in Hong Kong earlier this month.
The Chinese government reacted with anger, saying it was "totally wrong" to blame the authorities for the attacks, the source code of which originated in China.
It does operate a tight control over internet content, including pornography and sensitive political material, in what is dubbed the Great Firewall of China.
Earlier in the week Google blamed the great firewall for blocking its search service, although it said it did not know if it was a technical glitch or a deliberate act.
The issue is now resolved, a Google spokesman said in a statement.
"Interestingly our search traffic in China is now back to normal - even though we have not made any changes at our end. We will continue to monitor what is going on", he said.