A father and son were killed when a deep sinkhole swallowed their car on a major Mexican highway Wednesday morning, officials said.

Civil protection rescuers reached the rubble-covered Volkswagen Jetta lying on its roof at the bottom of the hole in the afternoon after working for more than eight hours on the closed section of road.

The sinkhole appeared before dawn, at around 6 a.m. A crane lowered rescuers into a yawning hole the width of two lanes in the middle of the highway. The initial hole was widened in order to build a ramp for recovery purposes.

Gerardo Ruiz Esparza, secretary of the federal Transportation Department, said the sinkhole was apparently caused by the erosion of a drain that runs more than 50 feet (15 meters) beneath the highway.

At a news conference at the site, Esparza blamed heavy rains during the past three days. He said a preliminary analysis indicated the rain caused a creek to swell beside the highway and blocked the drain with trash, contributing to the erosion.

According to a statement from the department, the highway was recently widened, but the existing drain was not thought to have been affected by this construction.

Esparza said later through Twitter that engineers would study the situation to determine responsibility.

The Mexico-Cuernavaca highway is the main highway connecting the capital to the Pacific coast resort city of Acapulco. It was unclear when the road would reopen.