South African authorities have detained three Chinese vessels and 100 crew members for allegedly illegal fishing in Indian Ocean waters off Port Elizabeth, officials said Monday.

The three ships were escorted into East London port after trying to flee from South African patrol vessels early on Sunday, and inspectors found about 600 tons of squid on board.

"The operation has resulted in capturing of three foreign vessels," said a joint statement from the agriculture ministry, maritime security agency and the defence forces.

The South African ships "had to increase speed in order to intercept the foreign fishing vessels which were speeding off," it added, saying the fishing vessels had no permits.

Sicelo Fayo, manager with the South African Maritime Safety Authority (SAMSA), confirmed to AFP that the three trawlers were Chinese.

The 96 sailors from the ships have been held for allegedly violating territorial waters regulations and illegal fishing.

Another Chinese vessel was held last week and its crew charged and fined for violating environmental laws, according to Fayo.

Fisheries Minister Senzeni Zokwana expressed concern at the growing poaching of fish off South Africa.

"We cannot tolerate the plundering of our marine resources," he said in the statement.

A study by environmental campaign group Greenpeace last year showed that Chinese-flagged or Chinese-owned fishing boats operating off Africa had soared in recent decades, from just 13 in 1985 to 462 in 2013.