Votes were being counted on Monday in what is expected to be Tanzania's tightest election race ever, with the governing party facing the first major challenge to its dominance in decades. But the opposition Chadema party have alleged fraud in Sunday's presidential, general and local elections. "There are allegations of electoral fraud," Chadema spokesman Tumaini Makene said late Sunday. John Magufuli of the long-ruling Chama Cha Mapinduzi (CCM) is seen as the narrow favorite to beat ex-prime minister Edward Lowassa, a CCM stalwart who recently defected to Chadema, which is heading a coalition of opposition parties. But analysts have warned that the unusually tight race could spark tensions, with the opposition providing the first credible challenge to the CCM since the introduction of multiparty democracy in 1995. Voting was delayed in some districts, including in some suburbs of the main city Dar es Salaam, after ballot papers were delayed, top National Elections Commission (NEC) official Kailima Ramadhani said. In the southwestern Sumbawanga region, "armed people attacked a vehicle hired by NEC and burned ballot papers," Ramadhani added, saying new voting dates for those districts would be organized. While voting otherwise passed off peacefully, senior Chadema official Mwesiga Baregu said they were concerned at reports of "a number of reported interceptions of stuffed (ballot)boxes." The opposition claims could not be independently verified, but Chadema said it was concerned, adding that police late Sunday arrested some party members at their tallying center. "We seem to be heading to results that may not be credible, and therefore might not be accepted not just by political parties, but will not be accepted by the voters themselves," Baregu said. British High Commissioner Dianna Melrose said she was generally impressed with the polls. "We witnessed thousands of people with high enthusiasm turning out and reporting at polling stations," Melrose said. "However, we are concerned with some cases where voting materials were delayed. This left many people frustrated." Election officials said they expect the results of the presidential race within three days, but some early results are expected to begin arriving on Monday. CCM election co-ordinator Yusuf Makamba criticised what he called the opposition's "inflammatory statements," warning that comments suggesting they might not accept officials results "may spark unrest." Many believe 55-year old Magufuli — currently minister of works, for which he earned the nickname "The Bulldozer" — will face a tough challenge from Lowassa, 62. Lowassa was prime minister from 2005 until his resignation in 2008 over corruption allegations that he denies, and has for years been a CCM loyalist, but on the campaign trail he called for an end to the party's rule. Outgoing President Jakaya Kikwete, who is not running having served his constitutional two-term limit, ordered the police to boost security to ensure calm in the country of 52 million people, of whom 22 million are registered to vote. As well as a presidential race, voters also cast ballots in parliamentary and local polls on Sunday, including on the semi-autonomous archipelago of Zanzibar, just off mainland Tanzania, which was holding its own presidential elections. Leading candidates in the Zanzibar vote are incumbent president Ali Mohamed Shein of the ruling CCM, and current vice-president Seif Sharif Hamad from the opposition Civic United Front (CUF), who share power in a unity government. Zanzibar has experienced sectarian and political tensions in recent years — including several grenade explosions — with the unrest affecting the islands' key tourist industry.