Three sailors have died and one is missing after their tugboat capsized while they were helping to clear a major oil spill off Mauritius.
Four others were rescued after the boat collided with a barge on Monday.
The accident happened two days after major protests in Mauritius over the government's handling of the clean up.
About 1,000 tonnes of oil spilled into a sanctuary for rare wildlife after the Japanese ship MV Wakashio struck a coral reef on 25 July.
Concern mounted further after 39 dead dolphins were found washed up on the shore last week. The cause of their deaths is not yet known but environmental campaigners believe it is linked to the spill and are demanding an inquiry.
The tugboat had been towing the unmanned barge back from the spill site in rough seas when the collision between them happened, the barge operator Taylor Smith Group said.
The eight crew members abandoned ship. Four were later rescued and taken to shore.
Prime Minister Pravind Jugnauth visited the rescued sailors in hospital and said rescue teams were searching for the missing crew members, the BBC's Yasine Mohabuth reports from the capital Port Louis.
Mr Jugnauth has promised an investigation into the accident.
His government has also promised to set up a commission to investigate the spill itself after coming under pressure over its handling of the incident.
Many Mauritians believe the government could have done more to prevent the spill. There is also criticism over the decision to deliberately sink part of the ship after it split in two.
Thousands of people marched through Port Louis on Saturday calling on the government to resign.
Many wore black and T-shirts with the inscription: "I love my country. I'm ashamed of my government." They waved the national flag, while honking horns and drumming.
One protester told the BBC: "They didn't do anything when the ship approached our coastline - 12 days they didn't do anything until the oil spill and now thousands of people and marine people are affected."
The captain of the ship has been arrested and charged with endangering safe navigation. He has not yet commented.