Two boats with 20 fishermen aboard were still missing while eight sailors from another sinking vessel were rescued in the South China Sea, maritime authorities said Monday.

In the latest case, 13 fishermen aboard a boat that went adrift -- due to engine failure -- in the waters 17 sea miles east off the southern island province Hainan at about 1 p.m. Monday, the South China Sea Rescue Bureau (SCSRB) said in a statement.

The Guangdong-registered fishing boat, a 17-meter wooden vessel, was en route from Hebo Port in Dianbai County, Guangdong, to Hainan, the bureau cited a family member surnamed Deng as saying in the statement.

Rescuers were not able to contact the fishermen, and rescue efforts were still under way, according to the statement.

Separately, the search for a fishing boat with seven people on board reported missing late Friday continued for the third day Monday.

The boat, registered in the port city of Zhanjiang, Guangdong, was heading to a port of Wenchang County in Hainan Province, rescue authorities said.

Family members had tried calling the fishermen, all of whom were from Zhanjiang, at around 9 p.m. Friday, only to find their cell phones off.

The rescue center and city fishery department in Zhanjiang dispatched 10 rescue vessels and a helicopter hours later to search for the vessel, but without success so far.

In another case, eight fishermen were rescued Monday before their damaged boat sank 40 sea miles southwest of Zhuhai, Guangdong Province, said a spokesman with the SCSRB under the Ministry of Transport.

The bureau dispatched an aircraft, B-7125, after receiving an emergency alert at about 9 a.m., according to the spokesman.

Seven fishermen were rescued and lifted to Zhuhai Jiuzhou Airport, while the eighth member of the crew swam away from the sinking vessel before the arrival of the aircraft and was picked up by a nearby fishing boat.

Maritime emergencies have occurred frequently in the South China Sea since Feb. 14 as the traditional "Season of Fog" lowered visibility to no more than three meters.

From Feb. 14 to 21, the SCSRB had rescued 55 people on board six vessels and retrieved one dead person from the water believed to have drowned.