Toronto fire crews are responding to a two-alarm blaze following reports of an explosion at a building in the downtown core.Toronto police say they were called about reports of a fire on the roof of a building under construction in the Richmond Street West and John Street area around 6 p.m. Friday. Video sent to CityNews shows plumes of smoke and at least one explosion on the rooftop of a building on Richmond Street.Other videos posted to social media show a fire burning on the rooftop of a building. window.plugins = {"ima3":{"ad_server_url":"http:\/\/pubads.g.doubleclick.net\/gampad\/ads?sz=640x360&iu=\/7326\/en.citynews_toronto.web\/video&ciu_szs=300x250&impl=s&gdfp_req=1&ad_rule=1&cmsid=1224&env=vp&output=xml_vast2&unviewed_position_start=1&url={window.location.href}&correlator={timestamp}&vid={mediainfo.id}&title={mediainfo.name}&referrer={document.referrer}&duration={mediainfo.duration}&description_url=toronto.citynews.ca","syndicated_enable":true,"index_bidding_ad_server_url_exchange":{"index_bidding_ad_exchange_site_id":{"preroll":{"1":{"1":{"siteID":191890},"2":{"siteID":192079}}}}}},"moat":{"partner_code":"rogersbrightcoveint878700116445"},"streamsense":{"ns_st_pu":"\"Rogers\"","c2":"3005682","c3":"\"CITYNEWS\"","ns_st_st":"\"CITYTV\"","ns_st_stc":"\"5193\""},"chartbeat":{"uid":"55711","domain":"toronto.citynews.ca"},"omniture":{"site_catalyst_account":"rogersrmiglobal","site_catalyst_brand":"citynews toronto"},"adtitle":{"advertisement_title":"Advertisement"}}“Information received that items are possibly exploding and debris may be falling onto the street below,” police said in a social media post. There were no immediate reports of injuries.Toronto police say Richmond Street West is closed between Peter Street and Duncan Street, and that pedestrian traffic is also being restricted in the area.More to come