Horror as truck mows down multiple pedestrians in downtown Boston

A truck has hit multiple pedestrians in downtown Boston, leaving two people in a critical condition including the driver. 

The horror crash unfolded around 12.45pm at Harrison and Kneeland Street in the Massachusetts city's Chinatown neighborhood.

Boston EMS said four people were taken to hospital with injuries, and two are in critical condition according to ABC affiliate WCVB. 

Two more people were treated at the scene but declined to be taken to hospital. 

An aerial photograph from the scene published by WCVB shows a yellow Penske truck overturned on a sidewalk with several firefighters stood close by.

Penske is an American company which provides truck rentals for moving home. 

Another image shows the truck overturned outside Great Wall Kitchen Supplies store and Jiro's Sushi, surrounded by debris strewn across the street. 

The vehicle was badly damaged by the impact, with the frontage crumpled.

Boston Police said it slammed into a building before overturning. 

Boston Fire Department said the truck also 'struck multiple poles' before it became 'wedged between a pole and the building'. 

'Firefighters used extrication tools to removed the trapped driver from the cab of truck,' the department added.  

'It was a bad accident, and hopefully those two people make it,' Boston Deputy Fire Chief Steven Shaffer told independent news station WHDH. 

Several emergency vehicles including ambulances, fire trucks, and police cruisers could be seen at the scene, which was cordoned off with police tape. 

The driver has not yet been identified. 

Boston Police Department issued an advisory warning that Kneeland Street between Washington Street and Tyler Street has been closed due to the crash 'with injuries'. 

'Please seek an alternative route', the department said.  

This is a breaking news story with updates to follow.