Police in Vietnam's capital have broken up a protest over what critics charge is the government's delayed response to massive fish deaths which they believe are linked to industrial pollution.

A protester, Le Hoang, said more than 30 people marched peacefully in downtown Hanoi for about 15 minutes on Sunday before most were taken to police stations in two buses. He said they were held for several hours and then released without charge.

Thousands of dead fish began washing ashore along more than 200 kilometers (120 miles) of shoreline in four central provinces in early April. Protesters and state media speculated that a steel complex owned by a subsidiary of Taiwan's Formosa Plastic Corp. may have been linked to what was an unprecedented environmental disaster for the Southeast Asian country.