A man dressed in hospital garb threw a toddler 30 feet from a pedestrian overpass onto a major highway, and the boy was later pronounced dead, authorities said.

A 23-year-old man was arrested Thursday after witnesses saw him throwing something, followed him and called police, authorities said. One or two vehicles may have struck the 2 1/2-year-old, but it was unclear exactly what killed him.

There were no reports of a missing child, police Capt. Frank Fujii said. Officers were contacting day-care centers and other area facilities to find out where the child came from.

"It's a sad incident. It's something we never wished happened," Fujii said.

The suspect was dressed in hospital clothes, with the bottoms cut off as shorts. It wasn't known whether he had come from a hospital, or which one, Fujii said.

Police temporarily closed the westbound lanes of the H-1 freeway, a major route into downtown Honolulu.