By Kathy Quiano and Sara Mazloumsaki, CNN

(CNN) -- Rescue crews have found 31 bodies, and are looking for 172 other people, after the ferry they were on collided Friday with a cargo ship in waters between southern Philippine islands, a Coast Guard official said.

Lt. Elgen Gregorio, from the Philippine Coast Guard, told CNN on Saturday morning that more than 600 people had been rescued. At that time, authorities were still looking for survivors.

The incident occurred around 9 p.m. Friday in the Mactan Channel about 2 miles northwest of Cebu City, the capital of Cebu province.

The passenger ship -- MV St. Thomas Aquinas -- was coming from nearby Butuan City and the cargo ship -- the Sulpicio, which had about 20 people aboard -- was leaving Cebu for the province of Davao in Mindanao.

The passenger ferry sank, but not before sending out a distress call heard by Coast Guard officials.

The cargo vessel involved in the crash -- along with Navy, Coast Guard and commercial vessels -- was helping in the rescue efforts.

At least 44 people were being treated at one hospital in Cebu.

The incident recalls one of the worst maritime disasters in world history dating to December 20, 1987, also off the Philippines.

Between 1,700 and more than 4,000 people were killed when the ferry Dona Paz collided with the tanker MT Victor. The number of casualties has varied; many claim the Dona Paz was extremely overcrowded.

CNN's Greg Botelho contributed to this report.