Eastland Network said all six lines of its 10kV transmission line from Wairoa to Gisborne were affected by the crash.
"Teams from the network are on the ground assessing the line but the 800 metre section affected has difficult access," a statement said.
The crew will work through the night.
Many homes and businesses, including Gisborne Hospital, are being run by generators.
Eastland Network general manager Brent Steward said residents should conserve power and water, and follow their home emergency plans.
The fire ban has been lifted to allow people to cook outside on an open fire if necessary.
He advised people to listen to the radio for further updates. Free barbecues are available at Waikanae Beach for cooking until they run out of gas.
BP Foster and Tyler Ormond Rd are operating currently and generators will be put into Caltex Gladstone Rd and BP Kaiti this afternoon.
Generators will also be put in at several fast food outlets.
The Rescue Co-ordination Centre received an emergency locator beacon transmitter alert from the agricultural plane shortly after 9am.
It is understood the aircraft is owned by Gisborne-based company Farmers Air.
The Farmers Air website says it provides a range of agricultural aviation application services - particularly aerial topdressing and fine particle application spraying.
"Safety is a critical part of our industry and operating safely with modern equipment allows us to deliver critical returns to our clientele,'' the site says.
News on hold for a day
Gisborne's local newspaper will not come out today because of the power cut.
The Gisborne Herald advised readers on its Facebook page.
"Our condolences to the families and friends of the victims."
NO NEWSPAPER TODAY
There will be no Gisborne Herald today because we have no power.
Power in Gisborne has been out...
Posted by The Gisborne Herald on Sunday, 11 December 2016
What you need to know
Power
• Treat lines as live at all times.
• Turn all power appliances off at the wall.
• Generators supplying the East Coast with power will be cut off from 2pm until 6pm, and again at 8pm.
• Generators are being installed at cellphone towers in the Gisborne district.
• People may experience some disruptions as generators are connected.
• Texting rather than phoning, saves power.
Water
• Save water both inside and out. That means limit the times the toilet is flushed. No watering of the garden.
Cooking and food
• Use gas for cooking either inside or outside on a barbecue.
• Fire ban has been lifted to enable people to cook outside on an open fire if necessary.
• The free barbecues at Waikanae Beach are available until they run out of gas or are refilled.
• Generators will go in at several fast food outlets later this afternoon.
• Generators will be put into several petrol and gas stations later this afternoon. These will be Caltex Gladstone Rd and BP Kaiti. BP Foster and Tyler Ormond Rd is not operating at the moment but hopes to be later this afternoon.
General
• Limit the times you open the freezer or fridge to help conserve your food.
Health
• Gisborne Hospital is open.
• Limit visits to the GP to urgent or emergency visits.
• People needing to boil water for baby formula could boil it on gas or a gas barbecue, or use bottled water.
Schools
• Parents should check with their schools as to whether they will be open tomorrow. • Wainui School was closed today because of the lack of water.
- Source: Tarawhiti Civil Defence Emergency Management
