The shooting at the American Civic Association stopped shortly after the first emergency calls came in at 10.30 am, but police did not enter the building until nearly 45 minutes later.

Survivors reported huddling for hours in a basement, not knowing whether they were still in danger after the gunman, 41-year-old Jiverly Wong, a Vietnamese immigrant, killed 13 people on Friday.

Medical examiners who conducted autopsies on the victims reported that their injuries were so severe, they would not have survived, he said.

Four Chinese were among those killed, and a Chinese student was also shot in the arm and leg but survived, officials said. The other victims came from Haiti (two), Pakistan (one), the Philippines (one), Iraq (one), Brazil (one), Vietnam (two, including the gunman) and the United States (two).

The first emergency calls came in at 10.30 am, Police Chief Joseph Zikuski told the news conference. The callers spoke broken English, and it took dispatchers two minutes to sort out what was happening, he said.

When police got there, the gunfire had stopped, so they believed there was no 'active gunman' in the centre and decided to wait for the commando team to arrive, Zikuski said.

Officials have said Wong was apparently upset about losing his job at a vacuum cleaner plant and about people picking on him for his limited English.

Wong was born in Vietnam to an ethnic Chinese family. He moved to the US in the early 1990s and soon afterward became a citizen, friends and relatives said.

Police and Wong's acquaintances portrayed him as an angry, troubled man who struggled with drugs and job loss and perhaps blamed his adopted country for his troubles. -- AP