The city's cultural centre has also come under mortar shelling.
At least 12 were killed both in the trolleybus and Donetsk city's centre shelling.
Fierce fighting between independence supporters and government troops in the region has already killed dozens and wounded over a hundred in the past week. At least 30 civilians were killed Saturday in a series of artillery attacks on the port city of Mariupol, with both sides trading blame for the violence.
At least 27 people died last week in attacks on the city of Donetsk, which has been under Ukrainian army rocket fire over the past few months.
Last spring, Kiev launched a military operation in southeastern Ukraine in response to local residents' refusal to recognize the new coup-installed government. A ceasefire agreement has been reached since then, but fighting continues in the region, leading to more civilian casualties.
The United Nations estimates that over 5,000 have been killed in the fighting, while some 1.4 million residents of southeastern Ukraine desperately need humanitarian assistance. According to the World Health Organization, hostilities have destroyed or led to the closure of half of the health care facilities in eastern Ukraine and over 70 percent of health workers have fled the region.