One other assailant described as a 28-year-old woman was injured in Liaoning, said a notice posted on a verified provincial government social media account.
Shenyang, the Liaoning capital where the incident happened, is almost 3,000 kilometres from Urumqi, the capital of Xinjiang, which has seen sporadic violence in recent years blamed by authorities on Islamist terrorists.
The restive region is home to most of China's 10 million Uighurs, a Turkic-speaking Muslim minority, who rights groups say face religious and cultural discrimination.
In one such incident, according to authorities, three people from a Xinjiang family crashed their car into crowds in Tiananmen Square, the symbolic heart of the Chinese state, killing themselves and two visitors in October 2013, raising the spectre of spreading violence.
In March 2014, 31 people were knifed to death by "Xinjiang separatists" in a mass stabbing at a train station in Kunming in the southwest, with four attackers killed.
All four alleged attackers in Shenyang were described as "Xinjiang terrorists", with the woman, whose name was given phonetically as Amanguli Maititusong, identified as a Uighur.
Three children who were with the attackers were removed by police, it added.
Clashes between authorities and alleged Islamist separatists - as well as attacks killing civilians - have spread in recent years, both in Xinjiang and outside it.
Rights groups say Uighurs suffer from religious repression and discrimination. Authorities have tightly restricted independent reporting on these incidents in the past.
Beijing launched a "strike hard" campaign in the province just over a year ago after an attack on a train station in Urumqi as Chinese President Xi Jinping was visiting the city.
The four adults attacked police with knives and blunt objects while "shouting jihadist slogans", according to the police.