Unidentified attackers fired on a Chinese cargo boat on the Mekong River in Laos, China's police said, less than two months after Beijing began joint patrols to protect shipping.

Shots were fired at the Chinese ship Sheng Tai 11 on Saturday evening, but none of the crew was wounded, China's Ministry of Public Security said in a statement on its website on Sunday.

The boat, which had five crew members, was carrying wood, Chinese state television reported.

China last month deployed more than 300 armed police to patrol the Mekong in boats in collaboration with Myanmar, Thailand and Laos after a deadly attack killed 13 Chinese sailors in October last year.

In the latest incident, the Chinese ship was returning to China from Thailand, the statement said.

After the attack occurred, patrol ships from both Laos and China responded and Laos was still pursuing those suspected of carrying out the shooting.

The Mekong flows through China's southwestern province of Yunnan into Southeast Asia, serving as a major trade route through several countries.

China reacted angrily to the October attack, sending patrol boats down the Mekong to retrieve 164 stranded Chinese sailors and 28 cargo ships and calling on diplomats from Thailand, Laos and Myanmar to speed up investigations.

Since then, police in Thailand have detained nine soldiers suspected of killing the Chinese sailors and are also thought to have links with a Myanmar drug kingpin.

In a separate incident earlier this month, an unidentified rebel group fired grenades targeting Myanmar soldiers on a patrol boat that was accompanying four Chinese cargo ships on the Mekong, but missed.