PHU QUOC ISLAND, Vietnam (Reuters/AFP) - A Vietnamese navy plane has spotted an object suspected of belonging to a Malaysian jetliner that went missing early on Saturday with 239 people on board, the Civil Aviation Authority of Vietnam said on its website on Sunday.

The authority said it was too dark to be certain the object was part of the missing plane, and that more aircraft would be dispatched to investigate the site, in waters off southern Vietnam, in the morning.

It was the first time that authorities had given any positive indication that traces of the Boeing 777, which disappeared in the early hours of Saturday morning, may have been discovered.

"We received information from a Vietnamese plane saying that they found two broken objects, which seem like those of an aircraft, located about 50 miles to the south-west of Tho Chu Island," said the senior from official from the National Committee for Search and Rescue, who did not want to be named.

"As it is night they cannot fish them out for proper identification. They have located the position of the areas and flown back to the land," he added. Planes and boats would be sent back to the area Monday to investigate further, he said.

Tho Chu island is part of a small archipelago off the south-western tip of Vietnam, which belongs to the country.

Two large oil slicks which authorities suspect were caused by jet fuel were detected late on Saturday further south off the island chain.