Leads indicate the Congress is likely to win 38 of the 68 seats. The BJP is leading in 23.
The Congress has held that the high voter turnout was a clear indication of an anti-incumbency vote. Congress leader five-time chief minister Virbhadra Singh thanked the people of the state and said, "I was asked to go back to the state and ensure a Congress win... who will become the next chief minister will be decided by the Congress high command, and president Sonia Gandhi."
The results are crucial for the future of Mr Singh, 78, who had to resign from the Union Cabinet over allegations of corruption. He was appointed the party's chief in the state just days before the polling.
Chief Minister Prem Kumar Dhumal said he will submit to whatever people will decide.
Opinion polls and analysts had given the Congress an edge in a state which has always voted against incumbency. No ruling party has retained power for two straight terms in Himachal.
Votes are being counted at 39 centres under heavy security. Being a smaller state with fewer seats than Gujarat, where counting is also underway, all results are expected by afternoon in Himachal.
Kangra district, the largest in the state with 15 seats, could play the decider in the elections. The region was dominated by the BJP in the last elections.
The Congress and the BJP are contesting all 68 seats. The Himachal Lokhit Party (HLP), formed by BJP rebel Maheshwar Singh, has put up candidates in 36 seats and could give a tough fight in Shimla, Kullu, Palampur and Jaswan Pragpur.
Of the total 459 candidates, a record number of 106 are independents. They and rebels, such as Congress legislator Yograj and former minister Ishwar Dass, could play spoilsport for the BJP and the Congress.
In the last elections in 2007, the BJP won by a landslide, winning 41 seats. The Congress had bagged 23 and the BSP one seat.