Police have lined up four rows deep to pay respects to a fellow officer who was among the victims of a gunman's rampage at a Manhattan office tower.

The New York police officer killed in a mass shooting in a Manhattan skyscraper on Monday was an immigrant who left behind a pregnant wife, two young sons and distraught parents, while friends and officials in Bangladesh and the United States described him as a hero.

Four people were killed and a fifth was injured in a mass shooting at a Midtown Manhattan office building on Monday.